Organometallic compound and organic light-emitting device including the same

ABSTRACT

Provided are the organometallic compound represented by Formula 1 and an organic light-emitting device including the same: 
     
       
         
         
             
             
         
       
         
         
           
             M, X 1  to X 4 , X 11 , ring CY 2  to ring CY 4 , T 1 , T 2 , R 1  to R 4 , and a1 to a4 in Formula 1 are the same as described in the present specification.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2019-0012817, filed on Jan. 31, 2019, and Korean Patent Application No. 10-2020-0008761, filed on Jan. 22, 2020, in the Korean Intellectual Property Office, the contents of which is incorporated herein in its entirety by reference.

BACKGROUND 1. Field

The present disclosure relates to an organometallic compound and an organic light-emitting device including the same.

2. Description of Related Art

Organic light-emitting devices are self-emission devices, which have improved characteristics in terms of viewing angles, response time, brightness, driving voltage, and response speed, and produce full-color images.

In an example, an organic light-emitting device includes an anode, a cathode, and an organic layer between the anode and the cathode, wherein the organic layer includes an emission layer. A hole transport region may be between the anode and the emission layer, and an electron transport region may be between the emission layer and the cathode. Holes provided from the anode may move toward the emission layer through the hole transport region, and electrons provided from the cathode may move toward the emission layer through the electron transport region. The holes and the electrons recombine in the emission layer to produce excitons. These excitons transit from an excited state to a ground state, thereby generating light.

SUMMARY

Provided are novel organometallic compounds, and organic light-emitting devices using the same.

Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments of the disclosure.

According to an aspect of an embodiment, an organometallic compound represented by Formula 1 is provided:

-   -   wherein, in Formula 1,     -   M is a transition metal,     -   X₁ may be C, and X₂ to X₄ may each independently be C or N,     -   a bond between X₁ and M may be a coordinate bond,     -   one of a bond between X₂ and M, a bond between X₃ and M, and a         bond between X₄ and M may be a coordinate bond, and the other         two bonds may be covalent bonds,     -   X₁₁ may be O, S, or N(R_(1a)),     -   ring CY₂ to ring CY₄ may each independently be a C₅-C₃₀         carbocyclic group or a C₁-C₃₀ heterocyclic group,     -   T₁ may be a single bond, a double bond, *—N(R₅)—*′, *—B(R₅)—*′,         *—P(R₅)—*′, *—C(R₅) (R₆)—*′, *—Si(R₅) (R₆)—*′, *—Ge(R₅) (R₆)—*′,         *—S—*′, *—Se—*′, *—O—*′, *—C(═O)—*′, *—S(═O)—*′, *—S(═O)₂—*′,         *—C(R₅)═*′, *═C(R₅)—*′, *—C(R₅)═C(R₆)—*′, *—C(═S)—*′, or         *—C≡C—*′,     -   T₂ may be a single bond, a double bond, *—N(R₇)—*′, *—B(R₇)—*′,         *—P(R₇)—*′, *—C(R₇) (R₈)—*′, *—Si(R₇) (R₈)—*′, *—Ge(R₇) (R₈)—*′,         *—S—*′, *—Se—*′, *—O—*′, *—C(═O)—*′, *—S(═O)—*′, *—S(═O)₂—*′,         *—C(R₇)═*′, *═C(R₇)—*′, *—C(R₇)═C(R₈)—*′, *—C(═S)—*′, or         *—C≡C—*′,     -   R_(1a) and R₁ to R₈ may each independently be hydrogen,         deuterium, —F, —Cl, —Br, —I, —SF₅, a hydroxyl group, a cyano         group, a nitro group, an amidino group, a hydrazine group, a         hydrazone group, a carboxylic acid group or a salt thereof, a         sulfonic acid group or a salt thereof, a phosphoric acid group         or a salt thereof, a substituted or unsubstituted C₁-C₆₀ alkyl         group, a substituted or unsubstituted C₂-C₆₀ alkenyl group, a         substituted or unsubstituted C₂-C₆₀ alkynyl group, a substituted         or unsubstituted C₁-C₆₀ alkoxy group, a substituted or         unsubstituted C₁-C₆₀ alkylthio group, a substituted or         unsubstituted C₃-C₁₀ cycloalkyl group, a substituted or         unsubstituted C₁-C₁₀ heterocycloalkyl group, a substituted or         unsubstituted C₃-C₁₀ cycloalkenyl group, a substituted or         unsubstituted C₂-C₁₀ heterocycloalkenyl group, a substituted or         unsubstituted C₆-C₆₀ aryl group, a substituted or unsubstituted         C₇-C₆₀ alkylaryl group, a substituted or unsubstituted C₆-C₆₀         aryloxy group, a substituted or unsubstituted C₆-C₆₀ arylthio         group, a substituted or unsubstituted C₁-C₆₀ heteroaryl group, a         substituted or unsubstituted C₂-C₆₀ alkyl heteroaryl group, a         substituted or unsubstituted monovalent non-aromatic condensed         polycyclic group, a substituted or unsubstituted monovalent         non-aromatic condensed heteropolycyclic group, —N(Q₁) (Q₂),         —Si(Q₃) (Q₄) (Q₅), —Ge(Q₃) (Q₄) (Q₅), —B(Q₆) (Q₇), —P(═O) (Q₈)         (Q₉), or —P(Q₈) (Q₉),     -   a1 may be an integer from 1 to 4,     -   a2 to a4 may each independently be an integer from 0 to 20,     -   at least one of R₁ in the number of a1 may each independently be         an unsubstituted or substituted C₁-C₆₀ alkyl group or an         unsubstituted or substituted C₃-C₁₀ cycloalkyl group,     -   two or more of a plurality of R₁(s) may optionally be linked to         each other to form a C₅-C₃₀ carbocyclic group unsubstituted or         substituted with at least one R_(10a) or a C₁-C₃₀ heterocyclic         group unsubstituted or substituted with at least one R_(10a),     -   two or more of a plurality of R₂(S) may optionally be linked to         each other to form a C₅-C₃₀ carbocyclic group unsubstituted or         substituted with at least one R_(10a) or a C₁-C₃₀ heterocyclic         group unsubstituted or substituted with at least one R_(10a),     -   two or more of a plurality of R₃(s) may optionally be linked to         each other to form a C₅-C₃₀ carbocyclic group unsubstituted or         substituted with at least one R_(10a) or a C₁-C₃₀ heterocyclic         group unsubstituted or substituted with at least one R_(10a),     -   two or more of a plurality of R₄(s) may optionally be linked to         each other to form a C₅-C₃₀ carbocyclic group unsubstituted or         substituted with at least one R_(10a) or a C₁-C₃₀ heterocyclic         group unsubstituted or substituted with at least one R_(10a),     -   two or more of R_(1a) and R₁ to R₈ may optionally be linked to         each other to form a C₅-C₃₀ carbocyclic group unsubstituted or         substituted with at least one R_(10a) or a C₁-C₃₀ heterocyclic         group unsubstituted or substituted with at least one R_(10a),     -   R_(10a) is the same as explained in connection with R₂,     -   * and *′ each indicate a binding site to a neighboring atom,     -   a substituent of the substituted C₁-C₆₀ alkyl group, the         substituted C₂-C₆₀ alkenyl group, the substituted C₂-C₆₀ alkynyl         group, the substituted C₁-C₆₀ alkoxy group, the substituted         C₁-C₆₀ alkylthio group, the substituted C₃-C₁₀ cycloalkyl group,         the substituted C₁-C₁₀ heterocycloalkyl group, the substituted         C₃-C₁₀ cycloalkenyl group, the substituted C₂-C₁₀         heterocycloalkenyl group, the substituted C₆-C₆₀ aryl group, the         substituted C₇-C₆₀ alkylaryl group, the substituted C₆-C₆₀         aryloxy group, the substituted C₆-C₆₀ arylthio group, the         substituted C₁-C₆₀ heteroaryl group, the substituted C₂-C₆₀         alkylheteroaryl group, the substituted monovalent non-aromatic         condensed polycyclic group, and the substituted monovalent         non-aromatic condensed heteropolycyclic group may be:     -   deuterium, —F, —Cl, —Br, —I, —CD₃, —CD₂H, —CDH₂, —CF₃, —CF₂H,         —CFH₂, a hydroxyl group, a cyano group, a nitro group, an amino         group, an amidino group, a hydrazine group, a hydrazone group, a         carboxylic acid group or a salt thereof, a sulfonic acid group         or a salt thereof, a phosphoric acid group or a salt thereof, a         C₁-C₆₀ alkyl group, a C₂-C₆₀ alkenyl group, a C₂-C₆₀ alkynyl         group, or a C₁-C₆₀ alkoxy group;     -   a C₁-C₆₀ alkyl group, a C₂-C₆₀ alkenyl group, a C₂-C₆₀ alkynyl         group, or a C₁-C₆₀ alkoxy group, each substituted with         deuterium, —F, —Cl, —Br, —I, —CD₃, —CD₂H, —CDH₂, —CF₃, —CF₂H,         —CFH₂, a hydroxyl group, a cyano group, a nitro group, an amino         group, an amidino group, a hydrazine group, a hydrazone group, a         carboxylic acid group or a salt thereof, a sulfonic acid group         or a salt thereof, a phosphoric acid group or a salt thereof, a         C₃-C₁₀ cycloalkyl group, a C₁-C₁₀ heterocycloalkyl group, a         C₃-C₁₀ cycloalkenyl group, a C₂-C₁₀ heterocycloalkenyl group, a         C₆-C₆₀ aryl group, a C₆-C₆₀ aryloxy group, a C₆-C₆₀ arylthio         group, a C₁-C₆₀ heteroaryl group, a monovalent non-aromatic         condensed polycyclic group, a monovalent non-aromatic condensed         heteropolycyclic group, —N(Q₁₁) (Q₁₂), —Si(Q₁₃) (Q₁₄) (Q₁₅),         —Ge(Q₁₃) (Q₁₄) (Q₁₅), —B(Q₁₆) (Q₁₇), —P(═O) (Q₁₈) (Q₁₉), —P(Q₁₈)         (Q₁₉), or any combination thereof;     -   a C₃-C₁₀ cycloalkyl group, a C₁-C₁₀ heterocycloalkyl group, a         C₃-C₁₀ cycloalkenyl group, a C₂-C₁₀ heterocycloalkenyl group, a         C₆-C₆₀ aryl group, a C₆-C₆₀ aryloxy group, a C₆-C₆₀ arylthio         group, a C₁-C₆₀ heteroaryl group, a monovalent non-aromatic         condensed polycyclic group, or a monovalent non-aromatic         condensed heteropolycyclic group, each unsubstituted or         substituted with deuterium, —F, —Cl, —Br, —I, —CD₃, —CD₂H,         —CDH₂, —CF₃, —CF₂H, —CFH₂, a hydroxyl group, a cyano group, a         nitro group, an amino group, an amidino group, a hydrazine         group, a hydrazone group, a carboxylic acid group or a salt         thereof, a sulfonic acid group or a salt thereof, a phosphoric         acid group or a salt thereof, a C₁-C₆₀ alkyl group, a C₂-C₆₀         alkenyl group, a C₂-C₆₀ alkynyl group, a C₁-C₆₀ alkoxy group, a         C₃-C₁₀ cycloalkyl group, a C₁-C₁₀ heterocycloalkyl group, a         C₃-C₁₀ cycloalkenyl group, a C₂-C₁₀ heterocycloalkenyl group, a         C₆-C₆₀ aryl group, a C₆-C₆₀ aryloxy group, a C₆-C₆₀ arylthio         group, a C₁-C₆₀ heteroaryl group, a monovalent non-aromatic         condensed polycyclic group, a monovalent non-aromatic condensed         heteropolycyclic group, —N(Q₂₁) (Q₂₂), —Si(Q₂₃) (Q₂₄) (Q₂₅),         —Ge(Q₂₃) (Q₂₄) (Q₂₅), —B(Q₂₆) (Q₂₇), —P(═O) (Q₂₈) (Q₂₉), —P(Q₂₈)         (Q₂₉), or any combination thereof;     -   —N(Q₃₁) (Q₃₂), —Si(Q₃₃) (Q₃₄) (Q₃₅), —Ge(Q₃₃) (Q₃₄) (Q₃₅),         —B(Q₃₆) (Q₃₇), —P(═O) (Q₃₈) (Q₃₉), or —P(Q₃₈) (Q₃₉); or     -   any combination thereof,     -   wherein Q₁ to Q₉, Q₁₁ to Q₁₉, Q₂₁ to Q₂₉ and Q₃₁ to Q₃₉ may each         independently be: hydrogen; deuterium; —F; —Cl; —Br; —I; a         hydroxyl group; a cyano group; a nitro group; an amidino group;         a hydrazine group; a hydrazone group; a carboxylic acid group or         a salt thereof; a sulfonic acid group or a salt thereof; a         phosphoric acid group or a salt thereof; a C₁-C₆₀ alkyl group         that is unsubstituted or substituted with deuterium, a C₁-C₆₀         alkyl group, a C₆-C₆₀ aryl group, or any combination thereof; a         C₂-C₆₀ alkenyl group; a C₂-C₆₀ alkynyl group; a C₁-C₆₀ alkoxy         group; a C₃-C₁₀ cycloalkyl group; a C₁-C₁₀ heterocycloalkyl         group; a C₃-C₁₀ cycloalkenyl group; a C₂-C₁₀ heterocycloalkenyl         group; a C₆-C₆₀ aryl group that is unsubstituted or substituted         with deuterium, a C₁-C₆₀ alkyl group, a C₆-C₆₀ aryl group, or         any combination thereof; a C₆-C₆₀ aryloxy group; a C₆-C₆₀         arylthio group; a C₁-C₆₀ heteroaryl group; a monovalent         non-aromatic condensed polycyclic group; or a monovalent         non-aromatic condensed heteropolycyclic group.

Another aspect provides an organic light-emitting device: including a first electrode; a second electrode; and an organic layer disposed between the first electrode and the second electrode and including an emission layer, wherein the organic layer includes at least one of the organometallic compound.

The organometallic compound in the emission layer of the organic layer may function as a dopant.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certain embodiments of the disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIGURE shows a schematic cross-sectional view of an organic light-emitting device according to an embodiment.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, the present embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the embodiments are merely described below, by referring to the figures, to explain aspects of the present description. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list.

It will be understood that when an element is referred to as being “on” another element, it can be directly on the other element or intervening elements may be present therebetween. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present.

It will be understood that, although the terms “first,” “second,” “third” etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, “a first element,” “component,” “region,” “layer” or “section” discussed below could be termed a second element, component, region, layer or section without departing from the teachings herein.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, “a,” “an,” “the,” and “at least one” do not denote a limitation of quantity, and are intended to cover both the singular and plural, unless the context clearly indicates otherwise. For example, “an element” has the same meaning as “at least one element,” unless the context clearly indicates otherwise.

“Or” means “and/or.” As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof.

Furthermore, relative terms, such as “lower” or “bottom” and “upper” or “top,” may be used herein to describe one element's relationship to another element as illustrated in the Figures. It will be understood that relative terms are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. For example, if the device in one of the figures is turned over, elements described as being on the “lower” side of other elements would then be oriented on “upper” sides of the other elements. The exemplary term “lower,” can therefore, encompasses both an orientation of “lower” and “upper,” depending on the particular orientation of the FIGURE. Similarly, if the device in one of the figures is turned over, elements described as “below” or “beneath” other elements would then be oriented “above” the other elements. The exemplary terms “below” or “beneath” can, therefore, encompass both an orientation of above and below.

“About” or “approximately” as used herein is inclusive of the stated value and means within an acceptable range of deviation for the particular value as determined by one of ordinary skill in the art, considering the measurement in question and the error associated with measurement of the particular quantity (i.e., the limitations of the measurement system). For example, “about” can mean within one or more standard deviations, or within ±30%, 20%, 10% or 5% of the stated value.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

Exemplary embodiments are described herein with reference to cross section illustrations that are schematic illustrations of idealized embodiments. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments described herein should not be construed as limited to the particular shapes of regions as illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, a region illustrated or described as flat may, typically, have rough and/or nonlinear features. Moreover, sharp angles that are illustrated may be rounded. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the precise shape of a region and are not intended to limit the scope of the present claims.

An organometallic compound according to an embodiment of the present disclosure may be represented by Formula 1 below:

-   -   M in Formula 1 may be a transition metal.

For example, M may be a first-row transition metal of the Periodic Table of Elements, a second-row transition metal of the Periodic Table of Elements, or a third-row transition metal of the Periodic Table of Elements.

In one or more embodiments, M may be Pt, Pd, Au, or Cu.

In Formula 1, X₁ may be C, and X₂ to X₄ may each independently be C or N.

In one or more embodiments, in Formula 1, X₂ and X₃ may each be C, and X₄ may be N.

A bond between X₁ and M in Formula 1 may be a coordinate bond.

In Formula 1, one of a bond between X₂ and M, a bond between X₃ and M, and a bond between X₄ and M may be a coordinate bond, and the other two bonds may be covalent bonds. Thus, the organometallic compound represented by Formula 1 may be electrically neutral.

In one or more embodiments, in Formula 1, a bond between X₂ and M and a bond between X₃ and M may be a covalent bond, and a bond between X₄ and M may be a coordinate bond.

-   -   X₁₁ in Formula 1 may be O, S, or N(R_(1a)).

In one or more embodiments, X₁₁ may be N(R_(1a)).

Ring CY₂ to ring CY₄ in Formula 1 may each independently be a C₅-C₃₀ carbocyclic group or a C₁-C₃₀ heterocyclic group.

For example, ring CY₂ to ring CY₄ may each independently be i) a first ring, ii) a second ring, iii) a condensed ring in which two or more first rings are condensed with each other, iv) a condensed ring in which two or more second rings are condensed with each other, or v) a condensed ring in which one or more first rings and one or more second rings are condensed with each other,

-   -   the first ring is a cyclopentane group, a cyclopentadiene group,         a furan group, a thiophene group, a pyrrole group, a silole         group, an indene group, an oxazole group, an isoxazole group, an         oxadiazole group, an isoxadiazole group, an oxatriazole group,         an isoxatriazole group, a thiazole group, an isothiazole group,         a thiadiazole group, an isothiadiazole group, a thiatriazole         group, an isothiatriazole group, a pyrazole group, an imidazole         group, a triazole group, a tetrazole group, an azasilole group,         a diazasilole group, or a triazasilole group, and     -   the second ring may be an adamantane group, a norbornane group,         a norbornene group, a cyclohexane group, a cyclohexene group, a         benzene group, a pyridine group, a pyrimidine group, a pyrazine         group, a pyridazine group, a triazine group, an oxazine group, a         thiazine group, a dihydropyrazine group, a dihydropyridine         group, or a dihydroazasilole group.

In one or more embodiments, ring CY₂ to ring CY₄ in Formula 1 may each independently be a benzene group, a naphthalene group, an anthracene group, a phenanthrene group, a triphenylene group, a pyrene group, a chrysene group, a cyclopentadiene group, a 1,2,3,4-tetrahydronaphthalene group, a thiophene group, a furan group, an indole group, a benzoborole group, a benzophosphole group, an indene group, a benzosilole group, a benzogermole group, a benzothiophene group, a benzoselenophene group, a benzofuran group, a carbazole group, a dibenzoborole group, a dibenzophosphole group, a fluorene group, a dibenzosilole group, a dibenzogermole group, a dibenzothiophene group, a dibenzoselenophene group, a dibenzofuran group, a dibenzothiophene 5-oxide group, a 9H-fluorene-9-one group, a dibenzothiophene 5,5-dioxide group, an azaindole group, an azabenzoborole group, an azabenzophosphole group, an azaindene group, an azabenzosilole group, an azabenzogermole group, an azabenzothiophene group, an azabenzoselenophene group, an azabenzofuran group, an azacarbazole group, an azadibenzoborole group, an azadibenzophosphole group, an azafluorene group, an azadibenzosilole group, an azadibenzogermole group, an azadibenzothiophene group, an azadibenzoselenophene group, an azadibenzofuran group, an azadibenzothiophene 5-oxide group, an aza-9H-fluorene-9-one group, an azadibenzothiophene 5,5-dioxide group, a pyridine group, a pyrimidine group, a pyrazine group, a pyridazine group, a triazine group, a quinoline group, an isoquinoline group, a quinoxaline group, a quinazoline group, a phenanthroline group, a pyrrole group, a pyrazole group, an imidazole group, a triazole group, an oxazole group, an isooxazole group, a thiazole group, an isothiazole group, an oxadiazole group, a thiadiazole group, a benzopyrazole group, a benzimidazole group, a benzoxazole group, a benzothiazole group, a benzoxadiazole group, a benzothiadiazole group, a 5,6,7,8-tetrahydroisoquinoline group, a 5,6,7,8-tetrahydroquinoline group, phenoxazine group, a phenothiazine group, a dihydrophenazine group, a dihydroacridine group, an azaphenoxazine group, an azaphenothiazine group, an azadihydrophenazine group, or an azadihydroacridine group.

In one or more embodiments, ring CY₂ may be a benzene group or a pyridine group, ring CY₃ may be a carbazole group, and ring CY₄ may be a pyridine group, a pyrimidine group, a pyrazine group, a pyridazine group, or a triazine group.

In Formula 1, T₁ may be a single bond, a double bond, *—N(R₅)—*′, *—B(R₅)—*′, *—P(R₅)—*′, *—C(R₅) (R₆)—*′, *—Si(R₅) (R₆)—*′, *—Ge(R₅) (R₆)—*′, *—S—*′, *—Se—*′, *—O—*′, *—C(═O)—*′, *—S(═O)—*′, *—S(═O)₂—*′, *—C(R₅)═*′, *═C(R₅)—*′, *—C(R₅)═C(R₆)—*′, *—C(═S)—*′, or *—C≡C—*′, and T₂ may be a single bond, a double bond, *—N(R₇)—*′, *—B(R₇)—*′, *—P(R₇)—*′, *—C(R₇) (R₈)—*′, *—Si(R₇) (R₈)—*′, *—Ge(R₇) (R₈)—*′, *—S—*′, *—Se—*′, *—O—*′, *—C(═O)—*′, *—S(═O)—*′, *—S(═O)₂—*′, *—C(R₇)═*′ *═C(R₇)—*′, *—C(R₇)═C(R₈)—*′, *—C(═S)—*′, or *—C≡C—*′. R₅ to R₈ are the same as described in the present specification.

In one or more embodiments, T₁ may be *—N(R₅)—*′, *—C(R₅) (R₆)—*′, *—S—*, *—O—*′ or *—S(═O)₂—*′, and T₂ may be a single bond, *—N(R₇)—*′, *—C(R₇) (R₈)—*′, *—S—*′, or *—O—*′.

R_(1a) and R₁ to R₈ in Formula 1 may each independently be hydrogen, deuterium, —F, —Cl, —Br, —I, —SF₅, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a substituted or unsubstituted C₁-C₆₀ alkyl group, a substituted or unsubstituted C₂-C₆₀ alkenyl group, a substituted or unsubstituted C₂-C₆₀ alkynyl group, a substituted or unsubstituted C₁-C₆₀ alkoxy group, a substituted or unsubstituted C₁-C₆₀ alkylthio group, a substituted or unsubstituted C₃-C₁₀ cycloalkyl group, a substituted or unsubstituted C₁-C₁₀ heterocycloalkyl group, a substituted or unsubstituted C₃-C₁₀ cycloalkenyl group, a substituted or unsubstituted C₂-C₁₀ heterocycloalkenyl group, a substituted or unsubstituted C₆-C₆₀ aryl group, a substituted or unsubstituted C₇-C₆₀ alkylaryl group, a substituted or unsubstituted C₆-C₆₀ aryloxy group, a substituted or unsubstituted C₆-C₆₀ arylthio group, a substituted or unsubstituted C₁-C₆₀ heteroaryl group, a substituted or unsubstituted C₂-C₆₀ alkyl heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, —N(Q₁) (Q₂), —Si(Q₃) (Q₄) (Q₅), —Ge(Q₃) (Q₄) (Q₅), —B(Q₆) (Q₇), —P(═O) (Q₈) (Q₉), or —P(Q₈) (Q₉). In this regard, Q₁ to Q₉ are the same as described in the present specification.

For example, R_(1a) and R₁ to R₈ in Formula 1 may each independently be:

-   -   hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano         group, a nitro group, an amino group, an amidino group, a         hydrazine group, a hydrazone group, a carboxylic acid group or a         salt thereof, a sulfonic acid group or a salt thereof, a         phosphoric acid group or a salt thereof, —SF₅, C₁-C₂₀ alkyl         group, a C₂-C₂₀ alkenyl group, a C₁-C₂₀ alkoxy group, or a         C₁-C₂₀ alkylthio group;     -   a C₁-C₂₀ alkyl group, a C₂-C₂₀ alkenyl group, a C₁-C₂₀ alkoxy         group, or a C₁-C₂₀ alkylthio group, each substituted with         deuterium, —F, —Cl, —Br, —I, —CD₃, —CD₂H, —CDH₂, —CF₃, —CF₂H,         —CFH₂, a hydroxyl group, a cyano group, a nitro group, an amino         group, an amidino group, a hydrazine group, a hydrazone group, a         carboxylic acid group or a salt thereof, a sulfonic acid group         or a salt thereof, a phosphoric acid group or a salt thereof, a         C₁-C₁₀ alkyl group, a cyclopentyl group, a cyclohexyl group, a         cycloheptyl group, a cyclooctyl group, an adamantanyl group, a         norbornanyl group, a norbornenyl group, a cyclopentenyl group, a         cyclohexenyl group, a cycloheptenyl group, a         bicyclo[1.1.1]pentyl group, a bicyclo[2.1.1]hexyl group, a         bicyclo[2.2.2]octyl group, a (C₁-C₂₀ alkyl)cyclopentyl group, a         (C₁-C₂₀ alkyl)cyclohexyl group, a (C₁-C₂₀ alkyl)cycloheptyl         group, a (C₁-C₂₀ alkyl)cyclooctyl group, a (C₁-C₂₀         alkyl)adamantanyl group, a (C₁-C₂₀ alkyl)norbornanyl group, a         (C₁-C₂₀ alkyl)norbornenyl group, a (C₁-C₂₀ alkyl)cyclopentenyl         group, a (C₁-C₂₀ alkyl)cyclohexenyl group, a (C₁-C₂₀         alkyl)cycloheptenyl group, a (C₁-C₂₀ alkyl)bicyclo[1.1.1]pentyl         group, a (C₁-C₂₀ alkyl)bicyclo[2.1.1]hexyl group, a (C₁-C₂₀         alkyl)bicyclo[2.2.2]octyl group, a phenyl group, a (C₁-C₂₀         alkyl)phenyl group, a biphenyl group, a terphenyl group, a         naphthyl group, a pyridinyl group, a pyrimidinyl group, or any         combination thereof;     -   a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a         cyclooctyl group, an adamantanyl group, a norbornanyl group, a         norbornenyl group, a cyclopentenyl group, a cyclohexenyl group,         a cycloheptenyl group, a bicyclo[1.1.1]pentyl group, a         bicyclo[2.1.1]hexyl group, a bicyclo[2.2.2]octyl group, a phenyl         group, a (C₁-C₂₀ alkyl)phenyl group, a biphenyl group, a         terphenyl group, a naphthyl group, a fluorenyl group, a         phenanthrenyl group, an anthracenyl group, a fluoranthenyl         group, a triphenylenyl group, a pyrenyl group, a chrysenyl         group, a pyrrolyl group, a thiophenyl group, a furanyl group, an         imidazolyl group, a pyrazolyl group, a thiazolyl group, an         isothiazolyl group, an oxazolyl group, an isoxazolyl group, a         pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a         pyridazinyl group, an isoindolyl group, an indolyl group, an         indazolyl group, a purinyl group, a quinolinyl group, an         isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl         group, a quinazolinyl group, a cinnolinyl group, a carbazolyl         group, a phenanthrolinyl group, a benzimidazolyl group, a         benzofuranyl group, a benzothiophenyl group, an         isobenzothiazolyl group, a benzoxazolyl group, an         isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an         oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a         dibenzothiophenyl group, a benzocarbazolyl group, a         dibenzocarbazolyl group, an imidazopyridinyl group, an         imidazopyrimidinyl group, an azacarbazolyl group, an         azadibenzofuranyl group, or an azadibenzothiophenyl group, each         unsubstituted or substituted with deuterium, —F, —Cl, —Br, —I,         —CD₃, —CD₂H, —CDH₂, —CF₃, —CF₂H, —CFH₂, a hydroxyl group, a         cyano group, a nitro group, an amino group, an amidino group, a         hydrazine group, a hydrazone group, a carboxylic acid group or a         salt thereof, a sulfonic acid group or a salt thereof, a         phosphoric acid group or a salt thereof, a C₁-C₂₀ alkyl group, a         deuterated C₂-C₂₀ alkyl group, a C₁-C₂₀ alkoxy group, a         cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a         cyclooctyl group, an adamantanyl group, a norbornanyl group, a         norbornenyl group, a cyclopentenyl group, a cyclohexenyl group,         a cycloheptenyl group, a bicyclo[1.1.1]pentyl group, a         bicyclo[2.1.1]hexyl group, a bicyclo[2.2.2]octyl group, a         (C₁-C₂₀ alkyl)cyclopentyl group, a (C₁-C₂₀ alkyl)cyclohexyl         group, a (C₁-C₂₀ alkyl)cycloheptyl group, a (C₁-C₂₀         alkyl)cyclooctyl group, a (C₁-C₂₀ alkyl)adamantanyl group, a         (C₁-C₂₀ alkyl)norbornanyl group, a (C₁-C₂₀ alkyl)norbornenyl         group, a (C₁-C₂₀ alkyl)cyclopentenyl group, a (C₁-C₂₀         alkyl)cyclohexenyl group, a (C₁-C₂₀ alkyl)cycloheptenyl group, a         (C₁-C₂₀ alkyl)bicyclo[1.1.1]pentyl group, a (C₁-C₂₀         alkyl)bicyclo[2.1.1]hexyl group, a (C₁-C₂₀         alkyl)bicyclo[2.2.2]octyl group, a phenyl group, a (C₁-C₂₀         alkyl)phenyl group, a biphenyl group, a terphenyl group, a         naphthyl group, a fluorenyl group, a phenanthrenyl group, an         anthracenyl group, a fluoranthenyl group, a triphenylenyl group,         a pyrenyl group, a chrysenyl group, a pyrrolyl group, a         thiophenyl group, a furanyl group, an imidazolyl group, a         pyrazolyl group, a thiazolyl group, an isothiazolyl group, an         oxazolyl group, an isoxazolyl group, a pyridinyl group, a         pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an         isoindolyl group, an indolyl group, an indazolyl group, a         purinyl group, a quinolinyl group, an isoquinolinyl group, a         benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl         group, a cinnolinyl group, a carbazolyl group, a phenanthrolinyl         group, a benzimidazolyl group, a benzofuranyl group, a         benzothiophenyl group, an isobenzothiazolyl group, a         benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group,         a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a         dibenzofuranyl group, a dibenzothiophenyl group, a         benzocarbazolyl group, a dibenzocarbazolyl group, an         imidazopyridinyl group, an imidazopyrimidinyl group, an         azacarbazolyl group, an azadibenzofuranyl group, an         azadibenzothiophenyl group, or any combination thereof; or     -   —N(Q₁) (Q₂), —Si(Q₃) (Q₄) (Q₅), —Ge(Q₃) (Q₄) (Q₅), —B(Q₆) (Q₇),         —P(═O) (Q₈) (Q₉), or —P(Q₈) (Q₉);

Q₁ to Q₉ may each independently be:

-   -   deuterium, —F, —CH₃, —CD₃, —CD₂H, —CDH₂, —CH₂CH₃, —CH₂CD₃,         —CH₂CD₂H, —CH₂CDH₂, —CHDCH₃, —CHDCD₂H, —CHDCDH₂, —CHDCD₃,         —CD₂CD₃, —CD₂CD₂H, —CD₂CDH₂, —CF₃, —CF₂H, —CFH₂, —CH₂CF₃,         —CH₂CF₂H, —CH₂CFH₂, —CHFCH₃, —CHFCF₂H, —CHFCFH₂, —CHFCF₃,         —CF₂CF₃, —CF₂CF₂H, or —CF₂CFH₂; or     -   an n-propyl group, an isopropyl group, an n-butyl group, a         sec-butyl group, an isobutyl group, a tert-butyl group, an         n-pentyl group, a tert-pentyl group, a neopentyl group, an         isopentyl group, a sec-pentyl group, 3-pentyl group, a         sec-isopentyl group, a phenyl group, a biphenyl group, or a         naphthyl group, each unsubstituted or substituted with         deuterium, —F, a C₁-C₁₀ alkyl group, a phenyl group, or any         combination thereof.     -   a1 in Formula 1 indicates the number of R₁(s), and may be an         integer from 1 to 4. For example, a1 may be 1 or 2. When a1 is         two or more, two or more of R₁(s) may be identical to or         different from each other.     -   a2 to a4 in Formula 1 indicate the numbers of R₂ to R₄,         respectively, and may each independently an integer from 0         to 20. When a2 is 2 or more, two or more R₂(s) may be identical         to or different from each other, when a3 is 2 or more, two or         more R₃(s) may be identical to or different from each other, and         when a4 is 2 or more, two or more R₄(s) may be identical to or         different from each other.

At least one of R₁ in the number of a1 in Formula 1 may each independently be an unsubstituted or substituted C₁-C₆₀ alkyl group or an unsubstituted or substituted C₃-C₁₀ cycloalkyl group.

In one or more embodiments, at least one of R₁(s) in the number of a1 in Formula 1 may each independently be a C₁-C₂₀ alkyl group or a C₃-C₁₀ cycloalkyl group, each unsubstituted or substituted with deuterium, —F, —Cl, —Br, —I, —CD₃, —CD₂H, —CDH₂, —CF₃, —CF₂H, —CFH₂, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C₁-C₁₀ alkyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a bicyclo[1.1.1]pentyl group, a bicyclo[2.1.1]hexyl group, a bicyclo[2.2.2]octyl group, a (C₁-C₂₀ alkyl)cyclopentyl group, a (C₁-C₂₀ alkyl)cyclohexyl group, a (C₁-C₂₀ alkyl)cycloheptyl group, a (C₁-C₂₀ alkyl)cyclooctyl group, a (C₁-C₂₀ alkyl)adamantanyl group, a (C₁-C₂₀ alkyl)norbornanyl group, a (C₁-C₂₀ alkyl)norbornenyl group, a (C₁-C₂₀ alkyl)cyclopentenyl group, a (C₁-C₂₀ alkyl)cyclohexenyl group, a (C₁-C₂₀ alkyl)cycloheptenyl group, a (C₁-C₂₀ alkyl)bicyclo[1.1.1]pentyl group, a (C₁-C₂₀ alkyl)bicyclo[2.1.1]hexyl group, a (C₁-C₂₀ alkyl)bicyclo[2.2.2]octyl group, or any combination thereof.

In one or more embodiments, at least one of R₁(s) in the number of a1 in Formula 1 may each independently a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, an isobutyl group, a tert-butyl group, an n-pentyl group, a tert-pentyl group, a neopentyl group, an isopentyl group, a sec-pentyl group, 3-pentyl group, a sec-isopentyl group, an n-hexyl group, an isohexyl group, a sec-hexyl group, a tert-hexyl group, an n-heptyl group, an isoheptyl group, a sec-heptyl group, a tert-heptyl group, an n-octyl group, an isooctyl group, a sec-octyl group, a tert-octyl group, an n-nonyl group, an isononyl group, a sec-nonyl group, a tert-nonyl group, an n-decyl group, an isodecyl group, a sec-decyl group, a tert-decyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a bicyclo[1.1.1]pentyl group, a bicyclo[2.1.1]hexyl group, a bicyclo[2.2.2]octyl group, a (C₁-C₂₀ alkyl)cyclopentyl group, a (C₁-C₂₀ alkyl)cyclohexyl group, a (C₁-C₂₀ alkyl)cycloheptyl group, a (C₁-C₂₀ alkyl)cyclooctyl group, a (C₁-C₂₀ alkyl)adamantanyl group, a (C₁-C₂₀ alkyl)norbornanyl group, a (C₁-C₂₀ alkyl)norbornenyl group, a (C₁-C₂₀ alkyl)cyclopentenyl group, a (C₁-C₂₀ alkyl)cyclohexenyl group, a (C₁-C₂₀ alkyl)cycloheptenyl group, a (C₁-C₂₀ alkyl)bicyclo[1.1.1]pentyl group, a (C₁-C₂₀ alkyl)bicyclo[2.1.1]hexyl group, or a (C₁-C₂₀ alkyl)bicyclo[2.2.2]octyl group, each unsubstituted or substituted with deuterium, —F, —Cl, —Br, —I, —CD₃, —CD₂H, —CDH₂, —CF₃, —CF₂H, —CFH₂, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, an isobutyl group, a tert-butyl group, an n-pentyl group, a tert-pentyl group, a neopentyl group, an isopentyl group, a sec-pentyl group, 3-pentyl group, a sec-isopentyl group, an n-hexyl group, an isohexyl group, a sec-hexyl group, a tert-hexyl group, an n-heptyl group, an isoheptyl group, a sec-heptyl group, a tert-heptyl group, an n-octyl group, an isooctyl group, a sec-octyl group, a tert-octyl group, an n-nonyl group, an isononyl group, a sec-nonyl group, a tert-nonyl group, an n-decyl group, an isodecyl group, a sec-decyl group, a tert-decyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a bicyclo[1.1.1]pentyl group, a bicyclo[2.1.1]hexyl group, a bicyclo[2.2.2]octyl group, a (C₁-C₂₀ alkyl)cyclopentyl group, a (C₁-C₂₀ alkyl)cyclohexyl group, a (C₁-C₂₀ alkyl)cycloheptyl group, a (C₁-C₂₀ alkyl)cyclooctyl group, a (C₁-C₂₀ alkyl)adamantanyl group, a (C₁-C₂₀ alkyl)norbornanyl group, a (C₁-C₂₀ alkyl)norbornenyl group, a (C₁-C₂₀ alkyl)cyclopentenyl group, a (C₁-C₂₀ alkyl)cyclohexenyl group, a (C₁-C₂₀ alkyl)cycloheptenyl group, a (C₁-C₂₀ alkyl)bicyclo[1.1.1]pentyl group, a (C₁-C₂₀ alkyl)bicyclo[2.1.1]hexyl group, a (C₁-C₂₀ alkyl)bicyclo[2.2.2]octyl group, or any combination thereof.

In one or more embodiments, R_(1a) and R₁ to R₈ in Formula 1 may each independently be hydrogen, deuterium, —F, —CH₃, —CD₃, —CD₂H, —CDH₂, —CF₃, —CF₂H, —CFH₂, a C₂-C₁₀ alkenyl group, a C₁-C₁₀ alkoxy group, a C₁-C₁₀ alkylthio group, a group represented by one of Formulae 9-1 to 9-39, a group represented by one of Formulae 9-1 to 9-39 in which at least one hydrogen is substituted with deuterium, a group represented by one of Formulae 9-201 to 9-237, a group represented by one of Formulae 9-201 to 9-237 in which at least one hydrogen is substituted with deuterium, a group represented by one of Formulae 10-1 to 10-129, a group represented by one of Formulae 10-1 to 10-129 in which at least one hydrogen is substituted with deuterium, a group represented by one of Formulae 10-201 to 10-350, a group represented by one of Formulae 10-201 to 10-350 in which at least one hydrogen is substituted with deuterium, —N(Q₁) (Q₂), —Si(Q₃) (Q₄) (Q₅), or —Ge(Q₃) (Q₄) (Q₅) (Q₃ to Q₅ are the same as described in the present specification).

In one or more embodiments, at least one of R₁(s) in the number of a1 may each independently be —CH₃, —CD₃, —CD₂H, —CDH₂, —CF₃, —CF₂H, —CFH₂, a group represented by one of Formulae 9-1 to 9-39, a group represented by one of Formulae 9-1 to 9-39 in which at least one hydrogen is substituted with deuterium, a group represented by one of Formulae 9-201 to 9-227, a group represented by one of Formulae 9-201 to 9-227 in which at least one hydrogen is substituted with deuterium, a group represented by one of Formulae 10-1 to 10-9, or a group represented by one of Formulae 10-1 to 10-9 in which at least one hydrogen is substituted with deuterium:

* in Formulae 9-1 to 9-39, 9-201 to 9-237, 10-1 to 10-129 and 10-201 to 10-350 indicates a binding site to a neighboring atom, Ph is a phenyl group, TMS is a trimethylsilyl group, and TMG is a trimethylgermyl group.

The terms “a group represented by one of Formulae 9-1 to 9-39 in which at least one hydrogen is substituted with deuterium” and “a group represented by one of Formulae 9-201 to 9-237 in which at least one hydrogen is substituted with deuterium” may be, for example, a group represented by one of Formulae 9-501 to 9-514 and 9-601 to 9-636:

The terms “a group represented by one of Formulae 10-1 to 10-129 in which at least one hydrogen is substituted with deuterium” and “a group represented by one of Formulae 10-201 to 10-350 in which at least one hydrogen is substituted with deuterium” may be, for example, a group represented by one of Formulae 10-501 to 10-553:

In one or more embodiments, in Formula 1, at least one of R₂(s) in the number of a2, at least one of R₄(s) in the number of a4, or any combination thereof may each independently be an unsubstituted or substituted C₁-C₆₀ alkyl group or an unsubstituted or substituted C₃-C₁₀ cycloalkyl group.

In one or more embodiments, in Formula 1, at least one of R₂(s) in the number of a2 may each independently be an unsubstituted or substituted C₁-C₆₀ alkyl group or an unsubstituted or substituted C₃-C₁₀ cycloalkyl group.

In one or more embodiments, in Formula 1, at least one of R₄(s) in the number of a4 may each independently be an unsubstituted or substituted C₁-C₆₀ alkyl group or an unsubstituted or substituted C₃-C₁₀ cycloalkyl group.

In one or more embodiments, in Formula 1, at least one of R₂(s) in the number of a2 and at least one of R₄(s) in the number of a4 may each independently be an unsubstituted or substituted C₁-C₆₀ alkyl group or an unsubstituted or substituted C₃-C₁₀ cycloalkyl group.

The organometallic compound represented by Formula 1 may satisfy one of Condition 1 to Condition 3 and/or, one of Condition 4 to Condition 6:

Condition 1

T₁ may be neither a single bond nor a double bond, a group represented by

may be a group represented by Formula A2-1, and a group represented by

may be a group represented by Formula A3-1 or A3-2.

Condition 2

T₁ may be a single bond or a double bond, a group represented by

may be a group represented by Formula A2-2, and a group represented by

may be a group represented by one of Formulae A3-1 or A3-2.

Condition 3

T₁ may be a single bond or a double bond, a group represented by

may be a group represented by Formula A2-1, and a group represented by

may be a group represented by Formula A3-3.

Condition 4

T₂ may be a single bond or a double bond, a group represented by

may be a group represented by Formula A3-2, and a group represented by

may be a group represented by Formula A4-1.

Condition 5

T₂ may be a single bond or a double bond, a group represented by

may be a group represented by Formulae A3-1 or A3-3, and a group represented by

may be a group represented by Formula A4-2.

Condition 6

T₂ may be neither a single bond nor a double bond, a group represented by

may be a group represented by Formulae A3-1 or A3-3, and a group represented by

may be a group represented by Formula A4-1.

In Formulae A2-1, A2-2, A3-1, A3-2, A3-3, A4-1, and A4-2,

-   -   X₂ to X₄, R₂ to R₄ and a2 to a4 are the same as described in the         present specification,     -   Z₂₁ to Z₂₃, Z₃₁ to Z₃₃, and Z₄₁ to Z₄₃ may each independently be         C or N,     -   a bond between Z₂₁ and X₂, a bond between X₂ and Z₂₂, a bond         between Z₂₂ and Z₂₃, a bond between Z₃₁ and X₃, a bond between         X₃ and Z₃₂, a bond between Z₃₁ and Z₃₃, a bond between Z₃₂ and         Z₃₃, a bond between Z₄₁ and X₄, a bond between X₄ and Z₄₂, and a         bond between Z₄₂ and Z₂₃ are each a chemical bond,     -   in Formulae A2-1 and A2-2, * indicates a binding site to M in         Formula 1, *′ indicates a binding site to a neighboring nitrogen         atom in Formula 1, and *″ indicates a binding site to T₁ in         Formula 1,     -   in Formulae A3-1 to A3-3, * indicates a binding site to M in         Formula 1, *″ indicates a binding site to T₁ in Formula 1, and         *′ indicates a binding site to T₂ in Formula 1, and     -   in Formulae A4-1 and A4-2, * indicates a binding site to M in         Formula 1, and *′ indicates a binding site to T₂ in Formula 1.

In one or more embodiments, a group represented by

in Formula 1 may be a group represented by one of Formulae A2-1 (1) to A2-1(17):

-   -   wherein, in Formulae A2-1 (1) to A2-1(17),     -   X₂ and R₂ are the same as described above,     -   X₂₁ is a single bond, O, S, N(R₂₁), C(R₂₁) (R₂₂), or Si(R₂₁)         (R₂₂), and X₂₂ is a single bond, O, S, N(R₂₃), C(R₂₃) (R₂₄), or         Si(R₂₃) (R₂₄), wherein at least one of X₂₁ and X₂₂ is not a         single bond,     -   R₂₁ to R₂₈ are the same as described in connection with R₂,     -   a25 may be an integer from 0 to 5,     -   a24 may be an integer from 0 to 4,     -   a23 may be an integer from 0 to 3,     -   a22 may be an integer from 0 to 2,     -   * indicates a binding site to M in Formula 1,     -   *′ indicates a binding site to a neighboring nitrogen atom in         Formula 1, and     -   *″ indicates a binding site to T₁ in Formula 1.

In one or more embodiments, a group represented by

in Formula 1 may be a group represented by one of Formulae A3-1(1) to A3-1(17) and A3-2(1) to A3-2(7):

-   -   wherein, in Formulae A3-1(1) to A3-1(17) and A3-2(1) to A3-2(7),     -   X₃ and R₃ are the same as described above,     -   X₃₁ may be single bond, O, S, N(R₃₁), C(R₃₁) (R₃₂), r Si(R₃₁)         (R₃₂), and X₃₂ may be a single bond, O, S, N(R₃₃), C(R₃₃) (R₃₄),         or Si(R₃₃) (R₃₄), and at least one of X₃₁ and X₃₂ of Formula         A3-1(16) and A3-1(17) may not be a single bond,     -   R₃₁ to R₃₈ are the same as described in connection with R₃,     -   a36 may be an integer from 0 to 6,     -   a35 may be an integer from 0 to 5,     -   a34 may be an integer from 0 to 4,     -   a33 may be an integer from 0 to 3,     -   a32 may be an integer from 0 to 2,     -   * indicates a binding site to M in Formula 1,     -   *′ indicates a binding site to T₂ in Formula 1,     -   *″ indicates a binding site to T₁ in Formula 1.

In one or more embodiments, a group represented by

in Formula 1 may be a group represented by one of Formulae A4-1(1) to A4-1(26) and A4-2(1) to A4-2(8):

-   -   wherein, in Formulae A4-1 (1) to A4-1(26) and A4-2(1) to         A4-2(8),     -   X₄ and R₄ are the same as described above,     -   X₄₁ may be a single bond, O, S, N(R₄₁), C(R₄₁) (R₄₂), or Si(R₄₁)         (R₄₂), and X₄₂ may be a single bond, O, S, N(R₄₃), C(R₄₃) (R₄₄),         or Si(R₄₃) (R₄₄), and at least one of X₄₁ and X₄₂ of Formula         A4-1(24) to A4-1(26) may not be a single bond,     -   R₄₁ to R₄₈ are the same as described in connection with R₄,     -   a46 may bean integer from 0 to 6,     -   a45 may be an integer from 0 to 5,     -   a44 may be an integer from 0 to 4,     -   a43 may be an integer from 0 to 3,     -   a42 may be an integer from 0 to 2,     -   * indicates a binding site to M in Formula 1, and     -   *′ indicates a binding site to T₂ in Formula 1.

In one or more embodiments, in Formula 1,

a group represented by

may be a group represented by one of Formulae CY1-1 to CY1-15, and/or a group represented by

may be a group represented by one of Formulae CY2-1 to CY2-8, and/or a group represented by

may be a group represented by one of Formulae CY3-1 to CY3-16, and/or

a group represented by

may be a group represented by one of Formulae CY4-1 to CY4-24:

-   -   wherein, in Formulae CY1-1 to CY1-15, CY2-1 to CY2-8, CY3-1 to         CY3-16, and CY4-1 to CY4-24,     -   X₁ to X₄, X₁₁ and R₁ to R₄ are each the same as described above,     -   X₃₁ may be a single bond, O, S, N(R₃₁), C(R₃₁) (R₃₂), or Si(R₃₁)         (R₃₂),     -   X₄₁ may be a single bond, O, S, N(R₄₁), C(R₄₁) (R₄₂), or Si(R₄₁)         (R₄₂),     -   R₁₁ to R₁₄ may each independently be a substituted or         unsubstituted C₁-C₆₀ alkyl group, or a substituted or         unsubstituted C₃-C₁₀ cycloalkyl group,     -   R₂₁ to R₂₃ are the same as described in connection with R₂, R₃₁         to R₃₆ are the same as described in connection with R₃, R₄₁ to         R₄₄ are the same as described in connection with R₄, and each of         R₂₁ to R₂₃, R₃₁ to R₃₆, and R₄₁ to R₄₄ is not hydrogen,

In Formulae CY1-1 to CY1-15, * indicates a binding site to M in Formula 1, and *′ indicates a binding site to ring CY₂ in Formula 1,

-   -   in Formulae CY2-1 to CY2-8, * indicates a binding site to M in         Formula 1, *′ indicates a binding site to a neighboring nitrogen         atom in Formula 1, and *″ indicates a binding site to T₁ in         Formula 1,     -   in Formulae CY3-1 to CY3-16, * indicates a binding site to M in         Formula 1, *″ indicates a binding site to T₁ in Formula 1, and         *′ indicates a binding site to T₂ in Formula 1, and     -   in Formulae CY4-1 to CY4-24, * indicates a binding site to M in         Formula 1, and *′ indicates a binding site to T₂ in Formula 1.

In one or more embodiments, in Formula 1,

-   -   a group represented by

may be a group represented by one of Formulae CY1-3 and CY1-8, and/or

-   -   a group represented by

may be a group represented by one of Formulae CY2-1 and CY2-3, and/or

-   -   a group represented by

may be a group represented by Formula CY3-1, and/or

-   -   a group represented by

may be a group represented by one of Formulae CY4-1 and CY4-4.

In one or more embodiments, the organometallic compound may be represented by one of Formulae 1A to 1C:

-   -   wherein, in Formulae 1A to 1C,     -   M, X₁ to X₄, X₁₁, T₁ and T₂ are the same as described above, and         T₂ in Formula 1C may not be a single bond,     -   Y₂₁ may be C(R₂₁) or N, Y₂₂ may be C(R₂₂) or N, Y₂₃ may be         C(R₂₃) or N, Y₃₁ may be C(R₃₁) or N, Y₃₂ may be C(R₃₂) or N, Y₃₃         may be C(R₃₃) or N, Y₃₄ may be C(R₃₄) or N, Y₃₅ may be C(R₃₅) or         N, Y₃₆ may be C(R₃₆) or N, Y₄₁ may be C(R₄₁) or N, Y₄₂ may be         C(R₄₂) or N, Y₄₃ may be C(R₄₃) or N, Y₄₄ may be C(R₄₄) or N, Y₄₅         may be C(R₄₅) or N, Y₄₆ may be C(R₄₆) or N, Y₄₇ may be C(R₄₇) or         N,     -   X₃₃ may be a single bond, O, S, N(R_(3a)), C(R_(3a)) (R_(3b)),         or Si(R_(3a)) (R_(3b)),     -   X₄₃ may be a single bond, O, S, N(R_(4a)), C(R_(4a)) (R_(4b)),         or Si(R_(4a)) (R_(4b)),     -   R₁₁ to R₁₄ are the same as described in connection with R₁, and         at least one of R₁₁ to R₁₄ may each independently be an         unsubstituted or substituted C₁-C₆₀ alkyl group or an         unsubstituted or substituted C₃-C₁₀ cycloalkyl group,     -   R₂₁ to R₂₃ may be the same as described in connection with R₂,         and two or more of R₂₁ to R₂₃ may optionally be linked to form a         C₅-C₃₀ carbocyclic group unsubstituted or substituted with at         least one R_(10a), or a C₁-C₃₀ heterocyclic group unsubstituted         or substituted with at least one R_(10a),     -   R₃₁ to R₃₆, R_(3a), and R_(3b) may be the same as described in         connection with R₃, and two or more of R₃₁ to R₃₆ may optionally         be linked to form a C₅-C₃₀ carbocyclic group unsubstituted or         substituted with at least one R_(10a) or a C₁-C₃₀ heterocyclic         group unsubstituted or substituted with at least one R_(10a),     -   R₄₁ to R₄₇, R_(4a), and R_(4b) may be the same as described in         connection with R₄, and two or more of R₄₁ to R₄₇ may optionally         be linked to form a C₅-C₃₀ carbocyclic group unsubstituted or         substituted with at least one R_(10a) or a C₁-C₃₀ heterocyclic         group unsubstituted or substituted with at least one R_(10a),         and     -   R_(10a) is the same as described in connection with R₂.

In one or more embodiments, R₁₁ to R₁₄ of Formula CY1-1 to CY1-15 and at least one of R₁₁ to R₁₄ of Formulae 1A to 1C may each independently be a C₁-C₂₀ alkyl group or a C₃-C₁₀ cycloalkyl group, each unsubstituted or substituted with deuterium, —F, —Cl, —Br, —I, —CD₃, —CD₂H, —CDH₂, —CF₃, —CF₂H, —CFH₂, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C₁-C₁₀ alkyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a bicyclo[1.1.1]pentyl group, a bicyclo[2.1.1]hexyl group, a bicyclo[2.2.2]octyl group, a (C₁-C₂₀ alkyl)cyclopentyl group, a (C₁-C₂₀ alkyl)cyclohexyl group, a (C₁-C₂₀ alkyl)cycloheptyl group, a (C₁-C₂₀ alkyl)cyclooctyl group, a (C₁-C₂₀ alkyl)adamantanyl group, a (C₁-C₂₀ alkyl)norbornanyl group, a (C₁-C₂₀ alkyl)norbornenyl group, a (C₁-C₂₀ alkyl)cyclopentenyl group, a (C₁-C₂₀ alkyl)cyclohexenyl group, a (C₁-C₂₀ alkyl)cycloheptenyl group, a (C₁-C₂₀ alkyl)bicyclo[1.1.1]pentyl group, a (C₁-C₂₀ alkyl)bicyclo[2.1.1]hexyl group, a (C₁-C₂₀ alkyl)bicyclo[2.2.2]octyl group, or any combination thereof.

In one or more embodiments, R₁₁ to R₁₄ of Formula CY1-1 to CY1-15 and at least one of R₁₁ to R₁₄ of Formulae 1A to 1C may each independently be a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, an isobutyl group, a tert-butyl group, an n-pentyl group, a tert-pentyl group, a neopentyl group, an isopentyl group, a sec-pentyl group, 3-pentyl group, a sec-isopentyl group, an n-hexyl group, an isohexyl group, a sec-hexyl group, a tert-hexyl group, an n-heptyl group, an isoheptyl group, a sec-heptyl group, a tert-heptyl group, an n-octyl group, an isooctyl group, a sec-octyl group, a tert-octyl group, an n-nonyl group, an isononyl group, a sec-nonyl group, a tert-nonyl group, an n-decyl group, an isodecyl group, a sec-decyl group, a tert-decyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a bicyclo[1.1.1]pentyl group, a bicyclo[2.1.1]hexyl group, a bicyclo[2.2.2]octyl group, a (C₁-C₂₀ alkyl)cyclopentyl group, a (C₁-C₂₀ alkyl)cyclohexyl group, a (C₁-C₂₀ alkyl)cycloheptyl group, a (C₁-C₂₀ alkyl)cyclooctyl group, a (C₁-C₂₀ alkyl)adamantanyl group, a (C₁-C₂₀ alkyl)norbornanyl group, a (C₁-C₂₀ alkyl)norbornenyl group, a (C₁-C₂₀ alkyl)cyclopentenyl group, a (C₁-C₂₀ alkyl)cyclohexenyl group, a (C₁-C₂₀ alkyl)cycloheptenyl group, a (C₁-C₂₀ alkyl)bicyclo[1.1.1]pentyl group, a (C₁-C₂₀ alkyl)bicyclo[2.1.1]hexyl group, or a (C₁-C₂₀ alkyl)bicyclo[2.2.2]octyl group, each unsubstituted or substituted with deuterium, —F, —Cl, —Br, —I, —CD₃, —CD₂H, —CDH₂, —CF₃, —CF₂H, —CFH₂, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, an isobutyl group, a tert-butyl group, an n-pentyl group, a tert-pentyl group, a neopentyl group, an isopentyl group, a sec-pentyl group, a 3-pentyl group, a sec-isopentyl group, an n-hexyl group, an isohexyl group, a sec-hexyl group, a tert-hexyl group, an n-heptyl group, an isoheptyl group, a sec-heptyl group, a tert-heptyl group, an n-octyl group, an isooctyl group, a sec-octyl group, a tert-octyl group, an n-nonyl group, an isononyl group, a sec-nonyl group, a tert-nonyl group, an n-decyl group, an isodecyl group, a sec-decyl group, a tert-decyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a bicyclo[1.1.1]pentyl group, a bicyclo[2.1.1]hexyl group, a bicyclo[2.2.2]octyl group, a (C₁-C₂₀ alkyl)cyclopentyl group, a (C₁-C₂₀ alkyl)cyclohexyl group, a (C₁-C₂₀ alkyl)cycloheptyl group, a (C₁-C₂₀ alkyl)cyclooctyl group, a (C₁-C₂₀ alkyl)adamantanyl group, a (C₁-C₂₀ alkyl)norbornanyl group, a (C₁-C₂₀ alkyl)norbornenyl group, a (C₁-C₂₀ alkyl)cyclopentenyl group, a (C₁-C₂₀ alkyl)cyclohexenyl group, a (C₁-C₂₀ alkyl)cycloheptenyl group, a (C₁-C₂₀ alkyl)bicyclo[1.1.1]pentyl group, a (C₁-C₂₀ alkyl)bicyclo[2.1.1]hexyl group, a (C₁-C₂₀ alkyl)bicyclo[2.2.2]octyl group, or any combination thereof.

In one or more embodiments, R₁₁ to R₁₄ of Formulae CY1-1 to CY1-15 and at least one of R₁₁ to R₁₄ of Formulae 1A to 1C may each independently be —CH₃, —CD₃, —CD₂H, —CDH₂, —CF₃, —CF₂H, —CFH₂, a group represented by one of Formulae 9-1 to 9-39, a group represented by one of Formulae 9-1 to 9-39 in which at least one hydrogen is substituted with deuterium, a group represented by one of Formulae 9-201 to 9-227, a group represented by one of Formulae 9-201 to 9-227 in which at least one hydrogen is substituted with deuterium, a group represented by one of Formulae 10-1 to 10-9, or a group represented by one of Formulae 10-1 to 10-9 in which at least one hydrogen is substituted with deuterium.

In one or more embodiments, in Formulae 1A and 1C, Y₂₁ may be C(R₂₁), Y₂₂ may be C(R₂₂), Y₂₃ may be C(R₂₃), Y₄₁ may be C(R₄₁), Y₄₂ may be C(R₄₂), Y₄₃ may be C(R₄₃), Y₄₄ may be C(R₄₄), and at least one of R₂₁ to R₂₃, at least one of R₄₁ to R₄₄, or any combination thereof may each be an unsubstituted or substituted C₁-C₆₀ alkyl group or an unsubstituted or substituted C₃-C₁₀ cycloalkyl group.

In one or more embodiments, in Formulae 1A to 1C, Y₂₁ may be C(R₂₁), Y₂₂ may be C(R₂₂), Y₂₃ may be C(R₂₃), and at least one of R₂₁ to R₂₃ may each independently be an unsubstituted or substituted C₁-C₆₀ alkyl group or an unsubstituted or substituted C₃-C₁₀ cycloalkyl group.

In one or more embodiments, in Formulae 1A and 1C, Y₄₁ may be C(R₄₁), Y₄₂ may be C(R₄₂), Y₄₃ may be C(R₄₃), Y₄₄ may be C(R₄₄), at least one of R₄₁ to R₄₄ may each independently be an unsubstituted or substituted C₁-C₆₀ alkyl group, or an unsubstituted or substituted C₃-C₁₀ cycloalkyl group.

In one or more embodiments, in Formulae 1A and 1C, Y₂₁ may be C(R₂₁), Y₂₂ may be C(R₂₂), Y₂₃ may be C(R₂₃), Y₄₁ may be C(R₄₁), Y₄₂ may be C(R₄₂), Y₄₃ may be C(R₄₃), Y₄₄ may be C(R₄₄), and at least one of R₂₁ to R₂₃ and at least one of R₄₁ to R₄₄ may each be an unsubstituted or substituted C₁-C₆₀ alkyl group or an unsubstituted or substituted C₃-C₁₀ cycloalkyl group.

In one or more embodiments, in Formula 1B, Y₂₁ may be C(R₂₁), Y₂₂ may be C(R₂₂), Y₂₃ may be C(R₂₃), Y₄₁ may be C(R₄₁), Y₄₂ may be C(R₄₂), Y₄₃ may be C(R₄₃), Y₄₄ may be C(R₄₄), Y₄₅ may be C(R₄₅), Y₄₆ may be C(R₄₆), Y₄₇ may be C(R₄₇), and at least one of R₂₁ to R₂₃, at least one of R₄₁ to R₄₇, or any combination thereof may each independently be an unsubstituted or substituted C₁-C₆₀ alkyl group or an unsubstituted or substituted C₃-C₁₀ cycloalkyl group.

In one or more embodiments, in Formula 1B, Y₄₁ may be C(R₄₁), Y₄₂ may be C(R₄₂), Y₄₃ may be C(R₄₃), Y₄₄ may be C(R₄₄), Y₄₅ may be C(R₄₅), Y₄₆ may be C(R₄₆), Y₄₇ may be C(R₄₇), and at least one of R₄₁ to R₄₇ may each independently be an unsubstituted or substituted C₁-C₆₀ alkyl group or an unsubstituted or substituted C₃-C₁₀ cycloalkyl group.

In one or more embodiments, in Formula 1B, Y₂₁ may be C(R₂₁), Y₂₂ may be C(R₂₂), Y₂₃ may be C(R₂₃), Y₄₁ may be C(R₄₁), Y₄₂ may be C(R₄₂), Y₄₃ may be C(R₄₃), Y₄₄ may be C(R₄₄), Y₄₅ may be C(R₄₅), Y₄₆ may be C(R₄₆), Y₄₇ may be C(R₄₇), and at least one of R₂₁ to R₂₃ and at least one of R₄₁ to R₄₇ may each independently be an unsubstituted or substituted C₁-C₆₀ alkyl group or an unsubstituted or substituted C₃-C₁₀ cycloalkyl group.

In Formula 1, i) two or more of a plurality of R₁(s) may optionally be linked to form a C₅-C₃₀ carbocyclic group unsubstituted or substituted with at least one R_(10a) or a C₁-C₃₀ heterocyclic group unsubstituted or substituted with at least one R_(10a), ii) two or more of a plurality of R₂(S) may optionally be linked to form a C₅-C₃₀ carbocyclic group unsubstituted or substituted with at least one R_(10a) or a C₁-C₃₀ heterocyclic group unsubstituted or substituted with at least one R_(10a), iii) two or more of a plurality of R₃(s) may optionally be linked to form a C₅-C₃₀ carbocyclic group unsubstituted or substituted with at least one R_(10a) or a C₁-C₃₀ heterocyclic group unsubstituted or substituted with at least one R_(10a), iv) two or more of a plurality of R₄(s) may optionally be linked to form a C₅-C₃₀ carbocyclic group unsubstituted or substituted with at least one R_(10a) or a C₁-C₃₀ heterocyclic group unsubstituted or substituted with at least one R_(10a), v) two or more of R_(1a) and R₁ to R₈ may optionally be linked to form a C₅-C₃₀ carbocyclic group unsubstituted or substituted with at least one R_(10a) or a C₁-C₃₀ heterocyclic group unsubstituted or substituted with at least one R_(10a), wherein “C₅-C₃₀ carbocyclic group” and “C₁-C₃₀ heterocyclic group” are the same as described in connection with ring CY₂, and R_(10a) is the same as described in connection with R₂.

The expressions * and *′ used herein each indicate a binding site to a neighboring atom, unless otherwise stated.

For example, the organometallic compound may be one of Compounds 1 to 120:

X₁ in Formula 1 may be C, and a bond between X₁ and M may be a coordinate bond. That is, X₁ in Formula 1 may be carbon of a carbene moiety. Since the metal-ligand bonding force in Formula 1 is enhanced due to the carbene moiety, which is a strong sigma-donating group, even when the organometallic compound represented by Formula 1 is in an excited state, the decomposition of the metal-ligand bond may be suppressed and thus, the organometallic compound represented by Formula 1 may have excellent durability.

Ring CY₁ in Formula 1 may be a condensed cyclic group (see Formula 1′) in which a benzene ring is condensed with a X₁-containing 5-membered ring. Accordingly, the organometallic compound represented by Formula 1 may have a relatively high triplet energy level, and thus, an electronic device including the organometallic compound represented by Formula 1, for example, an organic light-emitting device including the organometallic compound represented by Formula 1 may emit blue light and, at the same time, may have high luminescent efficiency and/or a long lifespan.

Furthermore, a1 in Formula 1 may be an integer from 1 to 4, and at least one of R₁(s) in the number of a1 may each independently be an unsubstituted or substituted C₁-C₆₀ alkyl group or an unsubstituted or substituted C₃-C₁₀ cycloalkyl group. Accordingly, the organometallic compound represented by Formula 1 may have a high optical orientation, and thus, for example, may emit blue light and at the same time, may have high luminescent efficiency.

For example, the HOMO, LUMO, and T₁ energy level of some of the compounds are structure-optimized at the (B3LYP, 6-31G(d,p)) level by using the DFT method of the Gaussian program and evaluated. Results thereof are shown in Table 1 below.

TABLE 1 Compound No. HOMO (eV) LUMO (eV) T₁ (eV) 1 −4.62 −1.27 2.63 2 −4.64 −1.27 2.66 3 −4.60 −1.25 2.64 4 −4.60 −1.25 2.64 5 −4.60 −1.25 2.64 6 −4.66 −1.29 2.65 7 −4.66 −1.29 2.66 8 −4.66 −1.29 2.66 9 −4.58 −1.16 2.62 10 −4.60 −1.19 2.57 11 −4.62 −1.27 2.64 12 −4.62 −1.27 2.64

From Table 1, it is confirmed that the organometallic compound represented by Formula 1 has such electric characteristics that are suitable for use as a dopant for an electronic device, for example, an organic light-emitting device.

For example, the organometallic compound represented by Formula 1 may emit blue light.

In one or more embodiments, the organometallic compound represented by Formula 1 may emit blue light having a maximum emission range of about 450 nm to about 470 nm, for example, about 457 nm to about 465 nm. Above maximum emission range may be confirmed by a photoluminescent (PL) spectrum and/or an electroluminescent (EL) spectrum for the organometallic compound represented by Formula 1.

In one or more embodiments, the triplet (T₁) energy level of the organometallic compound represented by Formula 1 may be 2.6 eV or more, or may have the range of about 2.6 eV to about 3.5 eV. The T₁ energy level is a result obtained by using a DFT method of Gaussian program (structure-optimized at the level of B3LYP, 6-31G(d,p)).

In one or more embodiments, the full width at half maximum (FWHM) of a main peak having a maximum intensity in the photoluminescent (PL) spectrum and/or an electroluminescent (EL) spectrum for the organometallic compound represented by Formula 1 may be 50 nm or less, in the range of about 10 nm to about 50 nm, in the range of about 15 nm to about 30 nm, or in the range of about 20 nm to about 30 nm.

Synthesis methods of the organometallic compound represented by Formula 1 may be understood by one of ordinary skill in the art by referring to Synthesis Examples provided below.

The organometallic compound represented by Formula 1 is suitable for use in an organic layer of an organic light-emitting device, for example, for use as a dopant in an emission layer of the organic layer. Thus, another aspect provides an organic light-emitting device that includes: a first electrode; a second electrode; and an organic layer disposed between the first electrode and the second electrode and including an emission layer, wherein the organic layer includes at least one organometallic compound represented by Formula 1.

Due to the inclusion of the organic layer having the organometallic compound represented by Formula 1, the organic light-emitting device may have improved driving voltage and improved external quantum efficiency.

The organometallic compound of Formula 1 may be used between a pair of electrodes of an organic light-emitting device. For example, the organometallic compound represented by Formula 1 may be included in the emission layer. In this regard, the organometallic compound may act as a dopant, and the emission layer may further include a host (that is, an amount of the organometallic compound represented by Formula 1 is smaller than an amount of the host). The emission layer may emit red light, green light, or blue light. For example, the organometallic compound may emit blue light.

For example, the emission layer may have a structure according to a first embodiment or a second embodiment:

First Embodiment

The emission layer may include the organometallic compound represented by Formula 1, and the organometallic compound may act as an emitter, for example, a phosphorescent emitter. For example, the ratio of the luminescent component emitted from the organometallic compound with respect to all luminescent components of the emission layer may be 80% or more, 85% or more, 90% or more, or 95% or more. Light emitted from the organometallic compound may be blue light.

Second Embodiment

The emission layer may further include, in addition to the organometallic compound represented by Formula 1, a phosphorescent dopant, a fluorescent dopant, or any combination thereof, each of which is different from the organometallic compound. In this regard, the organometallic compound may act as, not a phosphorescent emitter, a sensitizer or an auxiliary dopant. For example, the emission layer further includes a fluorescent dopant, the fluorescent dopant is different from the organometallic compound, and the ratio of the luminescent component emitted from the fluorescent dopant with respect to all luminescent components of the emission layer may be 80% or more, 85% or more, 90% or more, or 95% or more.

The amount of fluorescent dopant in the second embodiment may be, based on 100 parts by weight of the organometallic compound represented by Formula 1, in the range of about 1 part by weight to about 100 parts by weight, about 5 parts by weight to about 50 parts by weight, or about 10 parts by weight to about 20 parts by weight.

The total amount of the organometallic compound represented by Formula 1 and the fluorescent dopant in the second embodiment may be, based on 100 parts by weight of the emission layer, about 1 part by weight to about 30 parts by weight, about 3 parts by weight to about 20 parts by weight, or about 5 parts by weight to about 15 parts by weight.

The fluorescent dopant used in the second embodiment may not include a transition metal.

For example, the fluorescent dopant used in the second embodiment may be a fluorescence emission material that does not include a cyano group (—CN) and a fluoro group (—F).

In one or more embodiments, the fluorescent dopant used in the second embodiment may be a condensed cyclic group-containing compound, an amino group-containing compound, a styryl-containing compound, or a boron-containing compound.

For example, the fluorescent dopant used in the second embodiment may include an amino group-containing compound.

In one or more embodiments, the fluorescent dopant used in the second embodiment may include a naphthalene group, a fluorene group, a spiro-bifluorene group, a benzofluorene group, a dibenzofluorene group, a phenanthrene group, an anthracene group, a fluoranthene group, a triphenylene group, a pyrene group, a chrysene group, a naphthacene group, a picene group, a perylene group, a pentaphene group, an indenoanthracene group, a tetracene group, a group represented by one of Formulae 501-1 to 501-21, or any combination thereof:

In one or more embodiments, a fluorescent dopant used in the second embodiment may include a compound represented by Formula 501A or 501B:

-   -   wherein, in Formulae 501A and 501B,     -   Ar₅₀₁ may be a naphthalene group, a fluorene group, a         spiro-bifluorene group, a benzofluorene group, a dibenzofluorene         group, a phenanthrene group, an anthracene group, a fluoranthene         group, a triphenylene group, a pyrene group, a chrysene group, a         naphthacene group (a tetracene group), a picene group, a         perylene group, a pentaphene group, an indenoanthracene group, a         bisanthracene group, or a group represented by one of Formulae         501-1 to 501-21,     -   R₅₁₁ may be hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl         group, a nitro group, an amino group, an amidino group, a         hydrazine group, a hydrazone group, a carboxylic acid group or a         salt thereof, a sulfonic acid group or a salt thereof, a         phosphoric acid group or a salt thereof, a C₁-C₆₀ alkyl group, a         C₂-C₆₀ alkenyl group, a C₂-C₆₀ alkynyl group, a C₁-C₆₀ alkoxy         group, a C₃-C₁₀ cycloalkyl group, a C₁-C₁₀ heterocycloalkyl         group, a C₃-C₁₀ cycloalkenyl group, a C₂-C₁₀ heterocycloalkenyl         group, a C₆-C₆₀ aryl group, a C₆-C₆₀ aryloxy group, a C₆-C₆₀         arylthio group, a C₁-C₆₀ heteroaryl group, a monovalent         non-aromatic condensed polycyclic group, a monovalent         non-aromatic condensed heteropolycyclic group, or —Si(Q₅₀₁)         (Q₅₀₂) (Q₅₀₃),     -   xd5 may be an integer from 0 to 10,     -   L₅₀₁ to L₅₀₃ may each independently be:     -   a single bond; or     -   a C₃-C₁₀ cycloalkylene group, a C₁-C₁₀ heterocycloalkylene         group, a C₃-C₁₀ cycloalkenylene group, a C₂-C₁₀         heterocycloalkenylene group, a C₆-C₆₀ arylene group, a C₁-C₆₀         heteroarylene group, a divalent non-aromatic condensed         polycyclic group, or a divalent non-aromatic condensed         heteropolycyclic group, each unsubstituted or substituted with         deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a nitro group, an         amino group, an amidino group, a hydrazine group, a hydrazone         group, a carboxylic acid group or a salt thereof, a sulfonic         acid group or a salt thereof, a phosphoric acid group or a salt         thereof, a C₁-C₆₀ alkyl group, a C₂-C₆₀ alkenyl group, a C₂-C₆₀         alkynyl group, a C₁-C₆₀ alkoxy group, a C₃-C₁₀ cycloalkyl group,         a C₁-C₁₀ heterocycloalkyl group, a C₃-C₁₀ cycloalkenyl group, a         C₂-C₁₀ heterocycloalkenyl group, a C₆-C₆₀ aryl group, a C₆-C₆₀         aryloxy group, a C₆-C₆₀ arylthio group, a C₁-C₆₀ heteroaryl         group, a monovalent non-aromatic condensed polycyclic group, a         monovalent non-aromatic condensed heteropolycyclic group,         —Si(Q₅₀₁) (Q₅₀₂) (Q₅₀₃), or any combination thereof;     -   xd1 to xd3 may each independently be 1, 2, or 3,     -   R₅₀₁ and R₅₀₂ may each independently be a phenyl group, a         naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a         benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl         group, an anthracenyl group, a pyrenyl group, a chrysenyl group,         a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a         pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a         quinoxalinyl group, a quinazolinyl group, a carbazole group, a         triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl         group, or a dibenzosilolyl group, each unsubstituted or         substituted with deuterium, —F, —Cl, —Br, —I, a hydroxyl group,         a nitro group, an amino group, an amidino group, a hydrazine         group, a hydrazone group, a carboxylic acid group or a salt         thereof, a sulfonic acid group or a salt thereof, a phosphoric         acid group or a salt thereof, a C₁-C₆₀ alkyl group, a C₂-C₆₀         alkenyl group, a C₂-C₆₀ alkynyl group, a C₁-C₆₀ alkoxy group, a         C₃-C₁₀ cycloalkyl group, a C₁-C₁₀ heterocycloalkyl group, a         C₃-C₁₀ cycloalkenyl group, a C₂-C₁₀ heterocycloalkenyl group, a         C₆-C₆₀ aryl group, a C₆-C₆₀ aryloxy group, a C₆-C₆₀ arylthio         group, a C₁-C₆₀ heteroaryl group, a monovalent non-aromatic         condensed polycyclic group, a monovalent non-aromatic condensed         heteropolycyclic group, —Si(Q₅₀₁) (Q₅₀₂) (Q₅₀₃), or any         combination thereof,     -   Z₁₁ may be a C₁-C₆₀ alkyl group, a C₂-C₆₀ alkenyl group, a         C₂-C₆₀ alkynyl group, a C₁-C₆₀ alkoxy group, a C₃-C₁₀ cycloalkyl         group, a C₁-C₁₀ heterocycloalkyl group, a C₃-C₁₀ cycloalkenyl         group, a C₂-C₁₀ heterocycloalkenyl group, a C₆-C₆₀ aryl group, a         C₆-C₆₀ aryloxy group, a C₆-C₆₀ arylthio group, a C₁-C₆₀         heteroaryl group, a monovalent non-aromatic condensed polycyclic         group, or a monovalent non-aromatic condensed heteropolycyclic         group, each unsubstituted or substituted with deuterium, —F,         —Cl, —Br, —I, a hydroxyl group, a nitro group, an amino group,         an amidino group, a hydrazine group, a hydrazone group, a         carboxylic acid group or a salt thereof, a sulfonic acid group         or a salt thereof, a phosphoric acid group or a salt thereof, a         C₁-C₆₀ alkyl group, a C₂-C₆₀ alkenyl group, a C₂-C₆₀ alkynyl         group, a C₁-C₆₀ alkoxy group, a C₃-C₁₀ cycloalkyl group, a         C₁-C₁₀ heterocycloalkyl group, a C₃-C₁₀ cycloalkenyl group, a         C₂-C₁₀ heterocycloalkenyl group, a C₆-C₆₀ aryl group, a C₆-C₆₀         aryloxy group, a C₆-C₆₀ arylthio group, a C₁-C₆₀ heteroaryl         group, a monovalent non-aromatic condensed polycyclic group, a         monovalent non-aromatic condensed heteropolycyclic group,         —Si(Q₅₀₁) (Q₅₀₂) (Q₅₀₃), or any combination thereof,     -   xd4 may be 1, 2, 3, 4, 5, or 6, and     -   Q₅₀₁ to Q₅₀₃ may each independently be hydrogen, a C₁-C₆₀ alkyl         group, a C₁-C₆₀ alkoxy group, a C₆-C₆₀ aryl group, a C₁-C₆₀         heteroaryl group, a monovalent non-aromatic condensed polycyclic         group, or a monovalent non-aromatic condensed heteropolycyclic         group.

In one or more embodiments, the fluorescent dopant may include a compound represented by Formula 501A or 501B, and xd4 in Formula 501A may be 1, 2, 3, 4, 5, or 6, and xd4 in Formula 501B may be 2, 3, or 4.

In one or more embodiments, the fluorescent dopant may include one of Compounds FD(1) to FD(16), one of FD1 to FD15, or any combination thereof:

The expression “(an organic layer) includes at least one of organometallic compounds” used herein may include a case in which “(an organic layer) includes identical organometallic compounds represented by Formula 1” and a case in which “(an organic layer) includes two or more different organometallic compounds represented by Formula 1.”

For example, the organic layer may include, as the organometallic compound, only Compound 1. Here, Compound 1 may exist only in the emission layer of the organic light-emitting device. In one or more embodiments, the organic layer may include, as the organometallic compound, Compound 1 and Compound 2. In this regard, Compound 1 and Compound 2 may exist in an identical layer (for example, Compound 1 and Compound 2 all may exist in an emission layer).

The first electrode may be an anode, which is a hole injection electrode, and the second electrode may be a cathode, which is an electron injection electrode; or the first electrode may be a cathode, which is an electron injection electrode, and the second electrode may be an anode, which is a hole injection electrode.

In one or more embodiments, in the organic light-emitting device, the first electrode is an anode, and the second electrode is a cathode, and the organic layer further includes a hole transport region disposed between the first electrode and the emission layer and an electron transport region disposed between the emission layer and the second electrode, and the hole transport region includes a hole injection layer, a hole transport layer, an electron blocking layer, or any combination thereof, and the electron transport region includes a hole blocking layer, an electron transport layer, an electron injection layer, or any combination thereof.

The term “organic layer” used herein refers to a single layer and/or a plurality of layers between the first electrode and the second electrode of the organic light-emitting device. The “organic layer” may include, in addition to an organic compound, an organometallic complex including metal.

FIGURE is a schematic cross-sectional view of an organic light-emitting device 10 according to an embodiment. Hereinafter, the structure of an organic light-emitting device according to an embodiment and a method of manufacturing an organic light-emitting device according to an embodiment will be described in connection with FIGURE. The organic light-emitting device 10 includes a first electrode 11, an organic layer 15, and a second electrode 19, which are sequentially stacked.

A substrate may be additionally located under the first electrode 11 or above the second electrode 19. For use as the substrate, any substrate that is used in general organic light-emitting devices may be used, and the substrate may be a glass substrate or a transparent plastic substrate, each having excellent mechanical strength, thermal stability, transparency, surface smoothness, ease of handling, and water resistance.

In one or more embodiments, the first electrode 11 may be formed by depositing or sputtering a material for forming the first electrode 11 on the substrate. The first electrode 11 may be an anode. The material for forming the first electrode 11 may be selected from materials with a high work function to facilitate hole injection. The first electrode 11 may be a reflective electrode, a semi-transmissive electrode, or a transmissive electrode. The material for forming the first electrode 11 may be indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide (SnO₂), or zinc oxide (ZnO). In one or more embodiments, the material for forming the first electrode 11 may be metal, such as magnesium (Mg), aluminum (Al), aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium (Mg—In), or magnesium-silver (Mg—Ag).

The first electrode 11 may have a single-layered structure or a multi-layered structure including two or more layers. For example, the first electrode 11 may have a three-layered structure of ITO/Ag/ITO, but the structure of the first electrode 11 is not limited thereto.

The organic layer 15 is located on the first electrode 11.

The organic layer 15 may include a hole transport region, an emission layer, and an electron transport region.

The hole transport region may be between the first electrode 11 and the emission layer.

The hole transport region may include a hole injection layer, a hole transport layer, an electron blocking layer, a buffer layer, or any combination thereof.

The hole transport region may include only either a hole injection layer or a hole transport layer. In one or more embodiments, the hole transport region may have a hole injection layer/hole transport layer structure, a hole injection layer/hole transport layer/electron blocking layer structure, or a first hole injection layer/second hole injection layer/electron blocking layer structure, which, for each structure, are sequentially stacked in this stated order from the first electrode 11.

When the hole transport region includes a hole injection layer (HIL), the hole injection layer may be formed on the first electrode 11 by using one or more suitable methods, for example, vacuum deposition, spin coating, casting, and/or Langmuir-Blodgett (LB) deposition.

When a hole injection layer is formed by vacuum deposition, the deposition conditions may vary according to a material that is used to form the hole injection layer, and the structure and thermal characteristics of the hole injection layer. For example, the deposition conditions may include a deposition temperature of about 100 to about 500° C., a vacuum pressure of about 10⁻⁸ torr to about 10⁻³ torr, and a deposition rate of about 0.01 Å/sec to about 100 Å/sec. However, the deposition conditions are not limited thereto.

When the hole injection layer is formed using spin coating, coating conditions may vary according to the material used to form the hole injection layer, and the structure and thermal properties of the hole injection layer. For example, a coating speed may be from about 2,000 rpm to about 5,000 rpm, and a temperature at which a heat treatment is performed to remove a solvent after coating may be from about 80° C. to about 200° C. However, the coating conditions are not limited thereto.

Conditions for forming a hole transport layer and an electron blocking layer may be understood by referring to conditions for forming the hole injection layer.

The hole transport region may include m-MTDATA, TDATA, 2-TNATA, NPB, β-NPB, TPD, Spiro-TPD, Spiro-NPB, methylated-NPB, TAPC, HMTPD, 4,4′,4″-tris(N-carbazolyl)triphenylamine (TCTA), polyaniline/dodecylbenzenesulfonic acid (PANI/DBSA), poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS), polyaniline/camphor sulfonicacid (PANI/CSA), polyaniline/poly(4-styrenesulfonate) (PANI/PSS), a compound represented by Formula 201 below, a compound represented by Formula 202, or any combination thereof:

Ar₁₀₁ and Ar₁₀₂ in Formula 201 may each independently be a phenylene group, a pentalenylene group, an indenylene group, a naphthylene group, an azulenylene group, a heptalenylene group, an acenaphthylene group, a fluorenylene group, a phenalenylene group, a phenanthrenylene group, an anthracenylene group, a fluoranthenylene group, a triphenylenylene group, a pyrenylene group, a chrysenylenylene group, a naphthacenylene group, a picenylene group, a perylenylene group or a pentacenylene group, each unsubstituted or substituted with deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C₁-C₆₀ alkyl group, a C₂-C₆₀ alkenyl group, a C₂-C₆₀ alkynyl group, a C₁-C₆₀ alkoxy group, a C₃-C₁₀ cycloalkyl group, a C₃-C₁₀ cycloalkenyl group, a C₁-C₁₀ heterocycloalkyl group, a C₂-C₁₀ heterocycloalkenyl group, a C₆-C₆₀ aryl group, a C₆-C₆₀ aryloxy group, a C₆-C₆₀ arylthio group, a C₁-C₆₀ heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, or any combination thereof.

xa and xb in Formula 201 may each independently be an integer from 0 to 5, or 0, 1 or 2. For example, xa may be 1, and xb may be 0.

R₁₀₁ to R₁₀₈, R₁₁₁ to R₁₁₉ and R₁₂₁ to R₁₂₄ in Formulae 201 and 202 may each independently be:

-   -   hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano         group, a nitro group, an amino group, an amidino group, a         hydrazine group, a hydrazone group, a carboxylic acid group or a         salt thereof, a sulfonic acid group or a salt thereof, a         phosphoric acid group or a salt thereof, a C₁-C₁₀ alkyl group         (for example, a methyl group, an ethyl group, a propyl group, a         butyl group, a pentyl group, a hexyl group, and so on), or a         C₁-C₁₀ alkoxy group (for example, a methoxy group, an ethoxy         group, a propoxy group, a butoxy group, a pentoxy group, or so         on);     -   a C₁-C₁₀ alkyl group or a C₁-C₁₀ alkoxy group, each         unsubstituted or substituted with deuterium, —F, —Cl, —Br, —I, a         hydroxyl group, a cyano group, a nitro group, an amino group, an         amidino group, a hydrazine group, a hydrazone group, a         carboxylic acid group or a salt thereof, a sulfonic acid group         or a salt thereof, a phosphoric acid group or a salt thereof, or         any combination thereof; or     -   a phenyl group, a naphthyl group, an anthracenyl group, a         fluorenyl group or a pyrenyl group, each unsubstituted or         substituted with deuterium, —F, —Cl, —Br, —I, a hydroxyl group,         a cyano group, a nitro group, an amino group, an amidino group,         a hydrazine group, a hydrazone group, a carboxylic acid group or         a salt thereof, a sulfonic acid group or a salt thereof, a         phosphoric acid group or a salt thereof, a C₁-C₁₀ alkyl group, a         C₁-C₁₀ alkoxy group, or any combination thereof.

R₁₀₉ in Formula 201 may be a phenyl group, a naphthyl group, an anthracenyl group or a pyridinyl group, each unsubstituted or substituted with deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C₁-C₂₀ alkyl group, a C₁-C₂₀ alkoxy group, a phenyl group, a naphthyl group, an anthracenyl group, a pyridinyl group, or any combination thereof.

In one or more embodiments, a compound represented by Formula 201 may be represented by Formula 201A:

R₁₀₁, R₁₁₁, R₁₁₂, and R₁₀₉ in Formula 201A may be understood by referring to the description provided herein.

For example, the hole transport region may include one of compounds HT1 to HT20 or any combination thereof:

A thickness of the hole transport region may be from about 100 Å to about 10,000 Å, for example, about 100 Å to about 3,000 Å. When the hole transport region includes a hole injection layer, a hole transport layer, an electron blocking layer, or any combination thereof, a thickness of the hole injection layer may be in a range of about 100 Å to about 10,000 Å, for example, about 100 Å to about 1,000 Å, and a thickness of the hole transport layer may be in a range of about 50 Å to about 2,000 Å, for example, about 100 Å to about 1,500 Å. When the thicknesses of the hole transport region, the hole injection layer, and the hole transport layer are within these ranges, satisfactory hole transporting characteristics may be obtained without a substantial increase in driving voltage.

The hole transport region may further include, in addition to these materials, a charge-generation material for the improvement of conductive properties. The charge-generation material may be homogeneously or non-homogeneously dispersed in the hole transport region.

The charge-generation material may be, for example, a p-dopant. The p-dopant may be a quinone derivative, a metal oxide, a cyano group-containing compound, or any combination thereof, but embodiments of the present disclosure are not limited thereto. For example, the p-dopant may be a quinone derivative, such as tetracyanoquinonedimethane (TCNQ) or 2,3,5,6-tetrafluoro-tetracyano-1,4-benzoquinonedimethane (F4-TCNQ), or F6-TCNNQ; a metal oxide, such as a tungsten oxide or a molybdenum oxide; a cyano group-containing compound, such as Compound HT-D1 below, or any combination thereof.

The hole transport region may include a buffer layer.

Also, the buffer layer may compensate for an optical resonance distance according to a wavelength of light emitted from the emission layer, and thus, efficiency of a formed organic light-emitting device may be improved.

Meanwhile, when the hole transport region includes an electron blocking layer, a material for the electron blocking layer may be selected from materials for the hole transport region described above and materials for a host to be explained later. However, the material for the electron blocking layer is not limited thereto. For example, when the hole transport region includes an electron blocking layer, a material for the electron blocking layer may be mCP, which will be explained later.

Then, an emission layer (EML) may be formed on the hole transport region by vacuum deposition, spin coating, casting, LB deposition, or the like. When the emission layer is formed by vacuum deposition or spin coating, the deposition or coating conditions may be similar to those applied in forming the hole injection layer although the deposition or coating conditions may vary according to a material that is used to form the emission layer.

The emission layer may include a host and a dopant, and the dopant may include the organometallic compound represented by Formula 1 described in the present specification.

The host may include TPBi, TBADN, ADN (also referred to as “DNA”), CBP, CDBP, TCP, mCP, Compound H50, Compound H51, Compound H52, or any combination thereof:

When the organic light-emitting device is a full-color organic light-emitting device, the emission layer may be patterned into a red emission layer, a green emission layer, and/or a blue emission layer. In one or more embodiments, due to a stacked structure including a red emission layer, a green emission layer, and/or a blue emission layer, the emission layer may emit white light.

When the emission layer includes a host and a dopant, an amount of the dopant may be in a range of about 0.01 parts by weight to about 15 parts by weight based on 100 parts by weight of the host, but embodiments of the present disclosure are not limited thereto.

A thickness of the emission layer may be in a range of about 100 Å to about 1,000 Å, for example, about 200 Å to about 600 Å. When the thickness of the emission layer is within this range, excellent light-emission characteristics may be obtained without a substantial increase in driving voltage.

Then, an electron transport region may be located on the emission layer.

The electron transport region may include a hole blocking layer, an electron transport layer, an electron injection layer, or any combination thereof.

For example, the electron transport region may have a hole blocking layer/electron transport layer/electron injection layer structure or an electron transport layer/electron injection layer structure, but the structure of the electron transport region is not limited thereto. The electron transport layer may have a single-layered structure or a multi-layered structure including two or more different materials.

Conditions for forming the hole blocking layer, the electron transport layer, and the electron injection layer which constitute the electron transport region may be understood by referring to the conditions for forming the hole injection layer.

When the electron transport region includes a hole blocking layer, the hole blocking layer may include, for example, at least one of BCP, Bphen, and BAlq.

In one or more embodiment, the hole blocking layer may include the host, a material for an electron transport layer, a material for an electron injection layer, or any combination thereof, which will be described in detail.

A thickness of the hole blocking layer may be in a range of about 20 Å to about 1,000 Å, for example, about 30 Å to about 600 Å. When the thickness of the hole blocking layer is within these ranges, the hole blocking layer may have excellent hole blocking characteristics without a substantial increase in driving voltage.

The electron transport layer may include BCP, Bphen, TPBi, Alq₃, BAlq, TAZ, NTAZ, or any combination thereof:

In one or more embodiments, the electron transport layer may include at least one of ET1 to ET25:

A thickness of the electron transport layer may be from about 100 Å to about 1,000 Å, for example, about 150 Å to about 500 Å. When the thickness of the electron transport layer is within the range described above, the electron transport layer may have satisfactory electron transport characteristics without a substantial increase in driving voltage.

Also, the electron transport layer may further include, in addition to the materials described above, a metal-containing material.

The metal-containing material may include a Li complex. The Li complex may include, for example, Compound ET-D1 (LiQ) or ET-D2:

The electron transport region may include an electron injection layer (EIL) that promotes flow of electrons from the second electrode 19 thereinto.

The electron injection layer may include LiF, a NaCl, CsF, Li₂O, BaO, or any combination thereof.

A thickness of the electron injection layer may be in a range of about 1 Å to about 100 Å, and, for example, about 3 Å to about 90 Å. When a thickness of the electron injection layer is within these ranges, satisfactory electron injection characteristics may be obtained without substantial increase in driving voltage.

The second electrode 19 is located on the organic layer 15. The second electrode 19 may be a cathode. A material for forming the second electrode 19 may be metal, an alloy, an electrically conductive compound, or a combination thereof, which have a relatively low work function. For example, lithium (Li), magnesium (Mg), aluminum (Al), aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium (Mg—In), or magnesium-silver (Mg—Ag) may be formed as the material for forming the second electrode 19. To manufacture a top-emission type light-emitting device, a transmissive electrode formed using ITO or IZO may be used as the second electrode 19.

Hereinbefore, the organic light-emitting device has been described with reference to FIGURE, but embodiments of the present disclosure are not limited thereto.

Another aspect provides a diagnostic composition including at least one organometallic compound represented by Formula 1.

The organometallic compound represented by Formula 1 provides high luminescent efficiency. Accordingly, a diagnostic composition including the organometallic compound may have high diagnostic efficiency.

The diagnostic composition may be used in various applications including a diagnosis kit, a diagnosis reagent, a biosensor, and a biomarker.

The term “C₁-C₆₀ alkyl group” as used herein refers to a linear or branched saturated aliphatic hydrocarbon monovalent group having 1 to 60 carbon atoms, and examples thereof include a methyl group, an ethyl group, a propyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, an isoamyl group, and a hexyl group. The term “C₁-C₆₀ alkylene group” as used herein refers to a divalent group having the same structure as the C₁-C₆₀ alkyl group.

Examples of the C₁-C₆₀ alkyl group, the C₁-C₂₀ alkyl group, and/or the C₁-C₁₀ alkyl group are a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, an isobutyl group, a tert-butyl group, an n-pentyl group, a tert-pentyl group, a neopentyl group, an isopentyl group, a sec-pentyl group, 3-pentyl group, a sec-isopentyl group, an n-hexyl group, an isohexyl group, a sec-hexyl group, a tert-hexyl group, an n-heptyl group, an isoheptyl group, a sec-heptyl group, a tert-heptyl group, an n-octyl group, an isooctyl group, a sec-octyl group, a tert-octyl group, an n-nonyl group, an isononyl group, a sec-nonyl group, a tert-nonyl group, an n-decyl group, an isodecyl group, a sec-decyl group, and a tert-decyl group, each unsubstituted or substituted with a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, an isobutyl group, a tert-butyl group, an n-pentyl group, a tert-pentyl group, a neopentyl group, an isopentyl group, a sec-pentyl group, 3-pentyl group, a sec-isopentyl group, an n-hexyl group, an isohexyl group, a sec-hexyl group, a tert-hexyl group, an n-heptyl group, an isoheptyl group, a sec-heptyl group, a tert-heptyl group, an n-octyl group, an isooctyl group, a sec-octyl group, a tert-octyl group, an n-nonyl group, an isononyl group, a sec-nonyl group, a tert-nonyl group, an n-decyl group, an isodecyl group, a sec-decyl group, a tert-decyl group, or any combination thereof. For example, Formula 9-33 is a branched C₆ alkyl group, and may be a tert-butyl group substituted with two methyl groups.

The term “C₁-C₆₀ alkoxy group” used herein refers to a monovalent group represented by —OA₁₀₁ (wherein A₁₀₁ is the C₁-C₆₀ alkyl group), and examples thereof include a methoxy group, an ethoxy group, and an isopropyloxy group.

Examples of “a C₁-C₆₀ alkoxy group, a C₁-C₂₀ alkoxy group, or a C₁-C₁₀ alkoxy group” are a methoxy group, an ethoxy group, a propoxy group, a butoxy group, and a pentoxy group.

The term “C₁-C₆₀ alkylthio group” used herein refers to a monovalent group represented by —SA₁₀₁ (wherein A₁₀₁ is the C₁-C₆₀ alkyl group).

The term “C₂-C₆₀ alkenyl group” as used herein refers to a hydrocarbon group formed by substituting at least one carbon-carbon double bond in the middle or at the terminus of the C₂-C₆₀ alkyl group, and examples thereof include an ethenyl group, a propenyl group, and a butenyl group. The term “C₂-C₆₀ alkenylene group” as used herein refers to a divalent group having the same structure as the C₂-C₆₀ alkenyl group.

The term “C₂-C₆₀ alkynyl group” as used herein refers to a hydrocarbon group formed by substituting at least one carbon-carbon triple bond in the middle or at the terminus of the C₂-C₆₀ alkyl group, and examples thereof include an ethynyl group, and a propynyl group. The term “C₂-C₆₀ alkynylene group” as used herein refers to a divalent group having the same structure as the C₂-C₆₀ alkynyl group.

The term “C₃-C₁₀ cycloalkyl group” as used herein refers to a monovalent saturated hydrocarbon monocyclic group having 3 to 10 carbon atoms, and examples thereof include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, and a cycloheptyl group. The term “C₃-C₁₀ cycloalkylene group” as used herein refers to a divalent group having the same structure as the C₃-C₁₀ cycloalkyl group.

The term “C₃-C₁₀ cycloalkyl group” as used herein may include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a bicyclo[1.1.1]pentyl group(bicyclo[1.1.1]pentyl), a bicyclo[2.1.1]hexyl group(bicyclo[2.1.1]hexyl), a bicyclo[2.2.1]heptyl group(bicyclo[2.2.1]heptyl) (norbornanyl group), a bicyclo[2.2.2]octyl group, etc.

The term “C₁-C₁₀ heterocycloalkyl group” as used herein refers to a monovalent saturated monocyclic group having at least one N, O, P, Si, Se, Ge, B, S, or any combination thereof as a ring-forming atom and 1 to 10 carbon atoms, and examples thereof include a tetrahydrofuranyl group, and a tetrahydrothiophenyl group. The term “C₁-C₁₀ heterocycloalkylene group” as used herein refers to a divalent group having the same structure as the C₁-C₁₀ heterocycloalkyl group.

Examples of the term “C₁-C₁₀ heterocycloalkyl group” as used herein are a silolanyl group, a silinanyl group, a tetrahydrofuranyl group group, a tetrahydro-2H-pyranyl group, and a tetrahydrothiophenyl group.

The term “C₃-C₁₀ cycloalkenyl group” as used herein refers to a monovalent monocyclic group that has 3 to 10 carbon atoms and at least one carbon-carbon double bond in the ring thereof and no aromaticity, and examples thereof include a cyclopentenyl group, a cyclohexenyl group, and a cycloheptenyl group. The term “C₃-C₁₀ cycloalkenylene group” as used herein refers to a divalent group having the same structure as the C₃-C₁₀ cycloalkenyl group.

The term “C₂-C₁₀ heterocycloalkenyl group” as used herein refers to a monovalent monocyclic group that has at least one N, O, P, Si, Se, Ge, B, S, or any combination thereof as a ring-forming atom, 2 to 10 carbon atoms, and at least one double bond in its ring. Examples of the C₂-C₁₀ heterocycloalkenyl group are a 2,3-dihydrofuranyl group, and a 2,3-dihydrothiophenyl group. The term “C₂-C₁₀ heterocycloalkenylene group” as used herein refers to a divalent group having the same structure as the C₂-C₁₀ heterocycloalkenyl group.

The term “C₆-C₆₀ aryl group” as used herein refers to a monovalent group having a carbocyclic aromatic system having 6 to 60 carbon atoms, and the term “C₆-C₆₀ arylene group” as used herein refers to a divalent group having a carbocyclic aromatic system having 6 to 60 carbon atoms. Examples of the C₆-C₆₀ aryl group include a phenyl group, a naphthyl group, an anthracenyl group, a phenanthrenyl group, a pyrenyl group, and a chrysenyl group. When the C₆-C₆₀ aryl group and the C₆-C₆₀ arylene group each include two or more rings, the rings may be fused to each other.

The C₇-C₆₀ alkylaryl group used herein refers to a C₆-C₅₉ aryl group substituted with at least one C₁-C₅₄ alkyl group.

The term “C₁-C₆₀ heteroaryl group” as used herein refers to a monovalent group having a cyclic aromatic system that has at least one heteroatom selected from N, O, P, Si, Se, Ge, B, S, or any combination thereof as a ring-forming atom, and 1 to 60 carbon atoms. The term “C₁-C₆₀ heteroarylene group” as used herein refers to a divalent group having a cyclic aromatic system that has at least one heteroatom selected from N, O, P, Si, Se, Ge, B, S, or any combination thereof as a ring-forming atom, and 1 to 60 carbon atoms. Examples of the C₁-C₆₀ heteroaryl group include a pyridinyl group, a pyrimidinyl group, a pyrazinyl group, a pyridazinyl group, a triazinyl group, a quinolinyl group, and an isoquinolinyl group. When the C₆-C₆₀ heteroaryl group and the C₆-C₆₀ heteroarylene group each include two or more rings, the rings may be fused to each other.

The C₂-C₆₀ alkylheteroaryl group used herein refers to a C₁-C₅₉ heteroaryl group substituted with at least one C₁-C₅₉ alkyl group.

The term “C₆-C₆₀ aryloxy group” as used herein refers to —OA₁₀₂ (herein, A₁₀₂ is the C₆-C₆₀ aryl group), the term “C₆-C₆₀ arylthio group as used herein refers to —SA₁₀₃ (herein, A₁₀₃ is the C₆-C₆₀ aryl group), and the term “C₁-C₆₀ alkylthio group” as used herein refers to —SA₁₀₄ (herein, A₁₀₄ is the C₁-C₆₀ alkyl group).

The term “monovalent non-aromatic condensed polycyclic group” as used herein refers to a monovalent group (for example, having 8 to 60 carbon atoms) having two or more rings condensed to each other, only carbon atoms as ring-forming atoms, and no aromaticity in its entire molecular structure. Examples of the monovalent non-aromatic condensed polycyclic group include a fluorenyl group. The term “divalent non-aromatic condensed polycyclic group” as used herein refers to a divalent group having the same structure as that of the monovalent non-aromatic condensed polycyclic group.

The term “monovalent non-aromatic condensed heteropolycyclic group” as used herein refers to a monovalent group (for example, having 2 to 60 carbon atoms) having two or more rings condensed to each other, a heteroatom selected from N, O, P, Si, Se, Ge, B, S, or any combination thereof other than carbon atoms, as a ring-forming atom, and no aromaticity in its entire molecular structure. Examples of the monovalent non-aromatic condensed heteropolycyclic group include a carbazolyl group. The term “divalent non-aromatic condensed heteropolycyclic group” as used herein refers to a divalent group having the same structure as that of the monovalent non-aromatic condensed heteropolycyclic group.

The term “C₅-C₃₀ carbocyclic group” as used herein refers to a saturated or unsaturated cyclic group having, as a ring-forming atom, 5 to 30 carbon atoms only. The C₅-C₃₀ carbocyclic group may be a monocyclic group or a polycyclic group. The term “C₅-C₃₀ carbocyclic group (unsubstituted or substituted with at least one R_(10a))” used herein may include, for example, an adamantane group, a norbornene group, a bicyclo[1.1.1]pentane group, a bicyclo[2.1.1]hexane group, a bicyclo[2.2.1]heptane group(norbornane group), a bicyclo[2.2.2]octane group, a cyclopentane group, a cyclohexane group, a cyclohexene group, a benzene group, a naphthalene group, an anthracene group, a phenanthrene group, a triphenylene group, a pyrene group, a chrysene group, a 1,2,3,4-tetrahydronaphthalene group, a cyclopentadiene group, a silole group, and a fluorene group. each (unsubstituted or substituted with at least one R_(10a)).

The term “C₁-C₃₀ heterocyclic group” as used herein refers to a saturated or unsaturated cyclic group having, as a ring-forming atom, at least one heteroatom selected from N, O, Si, P, Se, Ge, B, S, or any combination thereof other than 1 to 30 carbon atoms. The C₁-C₃₀ heterocyclic group may be a monocyclic group or a polycyclic group. The term “C₁-C₃₀ heterocyclic group that is unsubstituted or substituted with at least one R_(10a)” may include, for example, a thiophene group, a furan group, a pyrrole group, a silole group, borole group, a phosphole group, a selenophene group, a germole group, a benzothiophene group, a benzofuran group, an indole group, an indene group, a benzosilole group, a benzoborole group, a benzophosphole group, a benzoselenophene group, a benzogermole group, a dibenzothiophene group, a dibenzofuran group, a carbazole group, a dibenzosilole group, a dibenzoborole group, a dibenzophosphole group, a dibenzoselenophene group, a dibenzogermole group, a dibenzothiophene 5-oxide group, a 9H-fluorene-9-one group, a dibenzothiophene 5,5-dioxide group, an azabenzothiophene group, an azabenzofuran group, an azaindole group, an azaindene group, an azabenzosilole group, an azabenzoborole group, an azabenzophosphole group, an azabenzoselenophene group, an azabenzogermole group, an azadibenzothiophene group, an azadibenzofuran group, an azacarbazole group, an azafluorene group, an azadibenzosilole group, an azadibenzoborole group, an azadibenzophosphole group, an azadibenzoselenophene group, an azadibenzogermole group, an azadibenzothiophene 5-oxide group, an aza-9H-fluorene-9-one group, an azadibenzothiophene 5,5-dioxide group, a pyridine group, a pyrimidine group, a pyrazine group, a pyridazine group, a triazine group, a quinoline group, an isoquinoline group, a quinoxaline group, a quinazoline group, a phenanthroline group, a pyrazole group, an imidazole group, a triazole group, an oxazole group, an isooxazole group, a thiazole group, an isothiazole group, an oxadiazole group, a thiadiazole group, a benzopyrazole group, a benzimidazole group, a benzoxazole group, a benzothiazole group, a benzoxadiazole group, a benzothiadiazole group, a 5,6,7,8-tetrahydroisoquinoline group, and a 5,6,7,8-tetrahydroquinoline group, each unsubstituted or substituted with at least one R_(10a).

The “deuterated C₂-C₂₀ alkyl group” may respectively be a C₂-C₂₀ alkyl group substituted with at least one deuterium. For example, the “deuterated C₂ alkyl group (that is, the deuterated ethyl group)” may include —CH₂CD₃, —CH₂CD₂H, —CH₂CDH₂, —CHDCD₃, —CHDCD₂H, —CHDCDH₂, —CD₂CD₃, —CD₂CD₂H, and —CD₂CDH₂. The “deuterated C₂-C₂₀ alkyl group” may be i) the case in which all hydrogen included in each group is substituted with deuterium, including a fully deuterated C₂-C₂₀ alkyl group, or ii) the case in which all hydrogen included in each group is substituted with deuterium, including a partially deuterated C₂-C₂₀ alkyl group.

The term “(C₁-C₂₀ alkyl) ‘X’ group” as used herein refers to a ‘X’ group substituted with at least one C₁-C₂₀ alkyl group. For example, the term “(C₁-C₂₀ alkyl)C₃-C₁₀ cycloalkyl group” refers to a C₃-C₁₀ cycloalkyl group substituted with at least one C₁-C₂₀ alkyl group, and the term “(C₁-C₂₀ alkyl)phenyl group” refers to a phenyl group substituted with at least one C₁-C₂₀ alkyl group. An example of the (C₁ alkyl)phenyl group is a toluyl group.

The terms “an azaindole group, an azabenzoborole group, an azabenzophosphole group, an azaindene group, an azabenzosilole group, an azabenzogermole group, an azabenzothiophene group, an azabenzoselenophene group, an azabenzofuran group, an azacarbazole group, an azadibenzoborole group, an azadibenzophosphole group, an azafluorene group, an azadibenzosilole group, an azadibenzogermole group, an azadibenzothiophene group, an azadibenzoselenophene group, an azadibenzofuran group, an azadibenzothiophene 5-oxide group, an aza-9H-fluorene-9-one group, and an azadibenzothiophene 5,5-dioxide group” each refers to a hetero ring obtained by substituting, with nitrogen, at least one carbon that forms the ring, and having the same backbone of a corresponding group selected from “an indole group, a benzoborole group, a benzophosphole group, an indene group, a benzosilole group, a benzogermole group, a benzothiophene group, a benzoselenophene group, a benzofuran group, a carbazole group, a dibenzoborole group, a dibenzophosphole group, a fluorene group, a dibenzosilole group, a dibenzogermole group, a dibenzothiophene group, a dibenzoselenophene group, a dibenzofuran group, a dibenzothiophene 5-oxide group, a 9H-fluorene-9-one group, and a dibenzothiophene 5,5-dioxide group.”

At least one substituent of the substituted C₅-C₃₀ carbocyclic group, the substituted C₂-C₃₀ heterocyclic group, the substituted C₁-C₆₀ alkyl group, the substituted C₂-C₆₀ alkenyl group, the substituted C₂-C₆₀ alkynyl group, the substituted C₁-C₆₀ alkoxy group, the substituted C₁-C₆₀ alkylthio group, the substituted C₃-C₁₀ cycloalkyl group, the substituted C₁-C₁₀ heterocycloalkyl group, the substituted C₃-C₁₀ cycloalkenyl group, the substituted C₂-C₁₀ heterocycloalkenyl group, the substituted C₆-C₆₀ aryl group, the substituted C₇-C₆₀ alkylaryl group, the substituted C₆-C₆₀ aryloxy group, the substituted C₆-C₆₀ arylthio group, the substituted C₁-C₆₀ heteroaryl group, the substituted C₂-C₆₀ alkyl heteroaryl group, the substituted monovalent non-aromatic condensed polycyclic group, and the substituted monovalent non-aromatic condensed heteropolycyclic group may each independently be:

-   -   deuterium, —F, —Cl, —Br, —I, —CD₃, —CD₂H, —CDH₂, —CF₃, —CF₂H,         —CFH₂, a hydroxyl group, a cyano group, a nitro group, an         amidino group, a hydrazine group, a hydrazone group, a         carboxylic acid group or a salt thereof, a sulfonic acid group         or a salt thereof, a phosphoric acid group or a salt thereof, a         C₁-C₆₀ alkyl group, a C₂-C₆₀ alkenyl group, a C₂-C₆₀ alkynyl         group, or a C₁-C₆₀ alkoxy group;     -   a C₁-C₆₀ alkyl group, a C₂-C₆₀ alkenyl group, a C₂-C₆₀ alkynyl         group, and a C₁-C₆₀ alkoxy group, each substituted with         deuterium, —F, —Cl, —Br, —I, —CD₃, —CD₂H, —CDH₂, —CF₃, —CF₂H,         —CFH₂, a hydroxyl group, a cyano group, a nitro group, an         amidino group, a hydrazine group, a hydrazone group, a         carboxylic acid group or a salt thereof, a sulfonic acid group         or a salt thereof, a phosphoric acid group or a salt thereof, a         C₃-C₁₀ cycloalkyl group, a C₁-C₁₀ heterocycloalkyl group, a         C₃-C₁₀ cycloalkenyl group, a C₂-C₁₀ heterocycloalkenyl group, a         C₆-C₆₀ aryl group, a C₇-C₆₀ alkylaryl group, a C₆-C₆₀ aryloxy         group, a C₆-C₆₀ arylthio group, a C₁-C₆₀ heteroaryl group, a         C₂-C₆₀ alkyl heteroaryl group, a monovalent non-aromatic         condensed polycyclic group, a monovalent non-aromatic condensed         heteropolycyclic group, —N(Q₁₁) (Q₁₂), —Si(Q₁₃) (Q₁₄) (Q₁₅),         —B(Q₁₆) (Q₁₇), —P(═O) (Q₁₈) (Q₁₉), —P(Q₁₈) (Q₁₉), or any         combination thereof;     -   a C₃-C₁₀ cycloalkyl group, a C₁-C₁₀ heterocycloalkyl group, a         C₃-C₁₀ cycloalkenyl group, a C₂-C₁₀ heterocycloalkenyl group, a         C₆-C₆₀ aryl group, a C₇-C₆₀ alkyl aryl group, a C₆-C₆₀ aryloxy         group, a C₆-C₆₀ arylthio group, a C₁-C₆₀ heteroaryl group, a         C₂-C₆₀ alkyl heteroaryl group, a monovalent non-aromatic         condensed polycyclic group, or a monovalent non-aromatic         condensed heteropolycyclic group, each unsubstituted or         substituted with deuterium, —F, —Cl, —Br, —I, —CD₃, —CD₂H,         —CDH₂, —CF₃, —CF₂H, —CFH₂, a hydroxyl group, a cyano group, a         nitro group, an amidino group, a hydrazine group, a hydrazone         group, a carboxylic acid group or a salt thereof, a sulfonic         acid group or a salt thereof, a phosphoric acid group or a salt         thereof, a C₁-C₆₀ alkyl group, a C₂-C₆₀ alkenyl group, a C₂-C₆₀         alkynyl group, a C₁-C₆₀ alkoxy group, a C₃-C₁₀ cycloalkyl group,         a C₁-C₁₀ heterocycloalkyl group, a C₃-C₁₀ cycloalkenyl group, a         C₂-C₁₀ heterocycloalkenyl group, a C₆-C₆₀ aryl group, a C₇-C₆₀         alkyl aryl group, a C₆-C₆₀ aryloxy group, a C₆-C₆₀ arylthio         group, a C₁-C₆₀ heteroaryl group, a C₂-C₆₀ alkyl heteroaryl         group, a monovalent non-aromatic condensed polycyclic group, a         monovalent non-aromatic condensed heteropolycyclic group,         —N(Q₂₁) (Q₂₂), —Si(Q₂₃) (Q₂₄) (Q₂₅), —B(Q₂₆) (Q₂₇), —P(═O) (Q₂₈)         (Q₂₉), —P(Q₂₈) (Q₂₉), or any combination thereof;     -   —N(Q₃₁) (Q₃₂), —Si(Q₃₃) (Q₃₄) (Q₃₅), —B(Q₃₆) (Q₃₇), —P(═O) (Q₃₈)         (Q₃₉), or —P(Q₃₈) (Q₃₉); or     -   any combination thereof;     -   wherein Q₁ to Q₉, Q₁₁ to Q₁₉, Q₂₁ to Q₂₉ and Q₃₁ to Q₃₉ may each         independently be: hydrogen; deuterium; —F; —C₁; —Br; —I; a         hydroxyl group; a cyano group; a nitro group; an amidino group;         a hydrazine group; a hydrazone group; a carboxylic acid group or         a salt thereof; a sulfonic acid group or a salt thereof; a         phosphoric acid group or a salt thereof; a C₁-C₆₀ alkyl group         that is unsubstituted or substituted with deuterium, a C₁-C₆₀         alkyl group, a C₆-C₆₀ aryl group, or any combination thereof; a         C₂-C₆₀ alkenyl group; a C₂-C₆₀ alkynyl group; a C₁-C₆₀ alkoxy         group; a C₃-C₁₀ cycloalkyl group; a C₁-C₁₀ heterocycloalkyl         group; a C₃-C₁₀ cycloalkenyl group; a C₂-C₁₀ heterocycloalkenyl         group; a C₆-C₆₀ aryl group that is unsubstituted or substituted         with deuterium, a C₁-C₆₀ alkyl group, a C₆-C₆₀ aryl group, or         any combination thereof; a C₆-C₆₀ aryloxy group; a C₆-C₆₀         arylthio group; a C₁-C₆₀ heteroaryl group; a monovalent         non-aromatic condensed polycyclic group; or a monovalent         non-aromatic condensed heteropolycyclic group.

Hereinafter, a compound and an organic light-emitting device according to embodiments are described in detail with reference to Synthesis Example and Examples. However, the organic light-emitting device is not limited thereto. The wording “B was used instead of A” used in describing Synthesis Examples means that an amount of A used was identical to an amount of B used, in terms of a molar equivalent.

EXAMPLES Synthesis Example 1 (Compound 2)

(1) Synthesis of Intermediate (A)

2-methoxy-9H-carbazole (15.0 g, 76.06 mmol), 2-bromo-4-(tert-butyl)pyridine (19.52 g, 91.27 mmol), copper (I) iodide (2.90 g, 15.21 mmol), 1,2-cyclohexyldiamine (3.47 g, 30.42 mmol), and K₃PO₄ (potassium phosphate tribasic) (32.31 g, 152.12 mmol) were mixed with 150 ml of 1,4-dioxane, and then, the mixture was stirred at a temperature of 120° C. for 18 hours. After the reaction was terminated, the mixture was cooled to room temperature, and an organic layer extracted by using saturated ammonium chloride (NH₄Cl) and dichloromethane (DCM). The DCM was dried using anhydrous magnesium sulfate (MgSO₄), followed by filtering, and condensing under reduced pressure. Silica gel column chromatography was performed on the crude product to produce Intermediate (A) (20.11 g, 60.85 mmol, and yield=80%).

LC-Mass (calculated: 330.17 g/mol, found: M⁺¹=331 g/mol).

(2) Synthesis of Intermediate (B)

Intermediate (A) (20.11 g, 60.85 mmol) and pyridine hydrochloride (70.3 g, 600.9 mmol) were stirred at a temperature of 190° C. for 18 hours. After the reaction was terminated, the mixture was cooled to room temperature, and an organic layer extracted by using saturated ammonium chloride (NH₄Cl) and dichloromethane (DCM). The DCM was dried using anhydrous magnesium sulfate (MgSO₄), followed by filtering, and condensing under reduced pressure. Silica gel column chromatography was performed on the crude product to produce Intermediate (B) (20.11 g, 60.85 mmol, and yield=80%).

LC-Mass (calculated: 316.16 g/mol, found: M⁺¹=317 g/mol).

(3) Synthesis of Intermediate (C)

5,6-dimethyl-1H-benzo[d]imidazole (15.0 g, 102.60 mmol), 1,3-dibromobenzene (24.20 g, 102.60 mmol), copper (I) iodide (3.91 g, 20.52 mmol), 1,10-phenanthroline (5.55 g, 30.78 mmol), and cesium carbonate (66.86 g, 205.20 mmol) were mixed with 250 ml of dimethylformamide (DMF), and then, the mixture was stirred at a temperature of 150° C. for 18 hours. After the reaction was terminated, the mixture was cooled to room temperature, and an organic layer extracted by using saturated ammonium chloride (NH₄Cl) and dichloromethane (DCM). The organic layer was dried using anhydrous magnesium sulfate (MgSO₄), followed by filtering, and condensing under reduced pressure. Silica gel column chromatography was performed on the crude product to produce Intermediate (C) (14.52 g, 48.22 mmol, yield=47%).

LC-Mass (calculated: 300.02 g/mol, found: M⁺¹=301 g/mol).

(4) Synthesis of Intermediate (D)

Intermediate (C) (5.0 g, 16.60 mmol), Intermediate (B) (5.25 g, 16.60 mmol), copper (I) iodide (0.63 g, 3.32 mmol), picolinic acid (0.82 g, 6.64 mmol), and potassium phosphate tribasic (7.05 g, 33.20 mmol) were mixed with 80 ml of dimethylsulfoxide (DMSO), and then, the mixture was stirred at a temperature of 120° C. for 18 hours. After the reaction was terminated, the mixture was cooled to room temperature, and an organic layer extracted by using saturated ammonium chloride (NH₄Cl) and ethyl acetate (EA). The organic layer was dried using anhydrous magnesium sulfate (MgSO₄), followed by filtering, and condensing under reduced pressure. Silica gel column chromatography was performed on the crude product to produce Intermediate (D) (5.35 g, 9.96 mmol, yield=60%).

LC-Mass (calculated: 536.26 g/mol, found: M⁺¹=537 g/mol).

(5) Synthesis of Intermediate (E)

Intermediate (D) (5.35 g, 9.96 mmol) and methyl iodide (4.24 g, 29.88 mmol) were mixed with 50 ml of toluene, and then, the mixture was stirred at a temperature of 60° C. for 12 hours. After the reaction was terminated, the mixture was cooled to room temperature, and then, silica gel column chromatography was performed on the crude product obtained by condensation under reduced pressure to produce Intermediate (E) (5.41 g, 7.97 mmol, yield=80%).

(6) Synthesis of Compound 2

Intermediate (E) (5.41 g, 7.97 mmol), Pt(COD)Cl₂ (3.28 g, 8.77 mmol), and sodium acetate (1.96 g, 23.91 mmol) were mixed with 80 ml of tetrahydrofuran (THF), and then, the mixture was stirred at a temperature of 120° C. for 48 hours. After the reaction was terminated, the mixture was cooled to room temperature, and an organic layer extracted by using saturated ammonium chloride (NH₄Cl) and EA. The organic layer was dried using anhydrous magnesium sulfate (MgSO₄), followed by filtering, and condensing under reduced pressure. Silica gel column chromatography was performed on the obtained result to produce Compound 2 (1.78 g, 2.39 mmol, yield=30%).

LC-Mass (calculated: 743.22 g/mol, found: M⁺¹=744 g/mol).

Synthesis Example 2 (Compound 3)

(1) Synthesis of Intermediate (F)

5,6-dimethyl-1H-benzo[d]imidazole (15.0 g, 102.60 mmol), 1,3-dibromo-5-(tert-butyl)benzene (30.0 g, 102.60 mmol), copper (I) iodide (3.91 g, 20.52 mmol), 1,10-phenanthroline (5.55 g, 30.78 mmol), and cesium carbonate (66.86 g, 205.20 mmol) were mixed with 250 ml of DMF, and then, the mixture was stirred at a temperature of 150° C. for 18 hours. After the reaction was terminated, the mixture was cooled to room temperature, and an organic layer extracted by using saturated ammonium chloride (NH₄Cl) and DCM. The organic layer was dried using anhydrous magnesium sulfate (MgSO₄), followed by filtering, and condensing under reduced pressure. Silica gel column chromatography was performed on the crude product to produce Intermediate (F) (17.60 g, 49.25 mmol, yield=48%).

LC-Mass (calculated: 356.09 g/mol, found: M⁺¹=357 g/mol).

(2) Synthesis of Intermediate (G)

Intermediate (F) (5.0 g, 14.0 mmol), Intermediate (B) (4.43 g, 14.0 mmol), copper (I) iodide (0.53 g, 2.80 mmol), picolinic acid (0.69 g, 5.60 mmol), and potassium phosphate tribasic (5.94 g, 28.0 mmol) were mixed with 70 ml of DMSO, and then, the mixture was stirred at a temperature of 120° C. for 18 hours. After the reaction was terminated, the mixture was cooled to room temperature, and an organic layer extracted by using saturated ammonium chloride (NH₄Cl) and ethyl acetate (EA). The organic layer was dried using anhydrous magnesium sulfate (MgSO₄), followed by filtering, and condensing under reduced pressure. Silica gel column chromatography was performed on the crude product to produce Intermediate (G) (5.23 g, 8.82 mmol, yield=63%).

LC-Mass (calculated: 592.32 g/mol, found: M⁺¹=593 g/mol).

(3) Synthesis of Intermediate (H)

Intermediate (G) (5.23 g, 8.82 mmol) and methyl iodide (3.76 g, 26.46 mmol) were mixed with 50 ml of toluene, and then, the mixture was stirred at a temperature of 60° C. for 12 hours. After the reaction was terminated, the mixture was cooled to room temperature, and then, silica gel column chromatography was performed on the crude product obtained by condensation under reduced pressure to produce Intermediate (E) (5.31 g, 7.23 mmol, yield=82%).

(4) Synthesis of Compound 3

Intermediate (H) (5.31 g, 7.23 mmol), Pt(COD)Cl₂ (2.98 g, 7.95 mmol), and sodium acetate (1.78 g, 21.69 mmol) were mixed with 75 ml of THF, and then, the mixture was stirred at a temperature of 120° C. for 48 hours. After the reaction was terminated, the mixture was cooled to room temperature, and an organic layer extracted by using saturated ammonium chloride (NH₄Cl) and EA. The organic layer was dried using anhydrous magnesium sulfate (MgSO₄), followed by filtering, and condensing under reduced pressure. Silica gel column chromatography was performed on the crude product to produce Compound 3 (2.02 g, 2.53 mmol, yield=35%).

LC-Mass (calculated: 743.22 g/mol, found: M⁺¹=744 g/mol).

Synthesis Example 3 (Compound 4)

(1) Synthesis of Intermediate (I)

Intermediate (G) (5.23 g, 8.82 mmol) and methyl iodide-d3 (3.84 g, 26.46 mmol) were mixed with 40 ml of toluene, and the mixture was stirred at a temperature of 60° C. for 12 hours. After the reaction was terminated, the mixture was cooled to room temperature, and then, silica gel column chromatography was performed on the result obtained by condensation under reduced pressure to produce Intermediate (I) (5.21 g, 7.06 mmol, yield=80%).

(2) Synthesis of Compound 4

Intermediate (I) (5.21 g, 7.06 mmol), Pt(COD)Cl₂ (2.91 g, 7.77 mmol), and sodium acetate (1.74 g, 21.18 mmol) were mixed with 70 ml of THF, and then, the mixture was stirred at a temperature of 120° C. for 48 hours. After the reaction was terminated, the mixture was cooled to room temperature, and an organic layer extracted by using saturated ammonium chloride (NH₄Cl) and EA. The organic layer was dried using anhydrous magnesium sulfate (MgSO₄), followed by filtering, and condensing under reduced pressure. Silica gel column chromatography was performed on the crude product to produce Compound 4 (2.10 g, 2.61 mmol, yield=37%).

Synthesis Example 4 (Compound 5)

(1) Synthesis of Intermediate (J)

5,6-dimethyl-1H-benzo[d]imidazole-d6 (15.6 g, 102.60 mmol), 1,3-dibromo-5-(tert-butyl)benzene (30.0 g, 102.60 mmol), copper (I) iodide (3.91 g, 20.52 mmol), 1,10-phenanthroline (5.55 g, 30.78 mmol), and cesium carbonate (66.86 g, 205.20 mmol) were mixed with 250 ml of DMF, and then, the mixture was stirred at a temperature of 150° C. for 18 hours. After the reaction was terminated, the mixture was cooled to room temperature, and an organic layer extracted by using saturated ammonium chloride (NH₄Cl) and DCM. The organic layer was dried using anhydrous magnesium sulfate (MgSO₄), followed by filtering, and condensing under reduced pressure. Silica gel column chromatography was performed on the crude product to produce Intermediate (J) (17.46 g, 48.22 mmol, yield=47%).

LC-Mass (calculated: 362.13 g/mol, found: M⁺¹=363 g/mol).

(2) Synthesis of Intermediate (K)

Intermediate (K) (5.02 g, 8.39 mmol, yield=61%) was obtained in the same manner as used to synthesize Intermediate (D) of Synthesis Example 1, except that Intermediate (J) (5.0 g, 13.76 mmol) was used instead of Intermediate (C).

LC-Mass (calculated: 598.81 g/mol, found: M⁺¹=599 g/mol).

(3) Synthesis of Intermediate (L)

Intermediate (L) (5.05 g, 6.79 mmol, yield=81%) was obtained in the same manner as used to synthesize Intermediate (I) of Synthesis Example 3, except that Intermediate (K) (5.02 g, 8.39 mmol) was used instead of Intermediate (G).

(4) Synthesis of Compound 5

Compound 5 (2.09 g, 2.58 mmol, yield=38%) was obtained in the same manner as used to synthesize Compound 2 of Synthesis Example 1, except that Intermediate (L) (5.05 g, 6.79 mmol) was used instead of Intermediate (E).

LC-Mass (calculated: 808.34 g/mol, found: M⁺¹=809 g/mol).

Synthesis Example 5 (Compound 9)

(1) Synthesis of Intermediate (M)

Intermediate (G) (5.0 g, 8.43 mmol), diphenyliodonium triflate (5.44 g, 12.65 mmol) and copper(II) acetate (0.15 g, 0.84 mmol) were mixed with 40 ml of DMF, and then, the mixture was stirred at a temperature of 100° C. for 12 hours. After the reaction was terminated, the mixture was cooled to room temperature, and an organic layer extracted by using saturated ammonium chloride (NH₄Cl) and DCM. The organic layer was dried using anhydrous magnesium sulfate (MgSO₄), followed by filtering, and condensing under reduced pressure. Silica gel column chromatography was performed on the crude product to produce Intermediate (M) (5.52 g, 6.74 mmol, yield=80%).

(2) Synthesis of Compound 9

Compound 9 (2.61 g, 3.03 mmol, yield=45%) was obtained in the same manner as used to synthesize Compound 2 of Synthesis Example 1, except that Intermediate (M) (5.52 g, 6.74 mmol) was used instead of Intermediate (E).

LC-Mass (calculated: 861.30 g/mol, found: M⁺¹=862 g/mol).

Synthesis Example 6 (Compound 14)

(1) Synthesis of Intermediate (N)

Intermediate (N) (13.50 g, 49.20 mmol, yield=82%) was obtained in the same manner as used to synthesize Intermediate (A) of Synthesis Example 1, except that 2-bromopyridine (11.38 g, 72 mmol) was used instead of 2-bromo-4-(tert-butyl)pyridine.

LC-Mass (calculated: 274.11 g/mol, found: M⁺¹=275 g/mol).

(2) Synthesis of Intermediate (O)

Intermediate (O) (10.62 g, 40.84 mmol, yield=83%) was obtained in the same manner as used to synthesize Intermediate (B) of Synthesis Example 1, except that Intermediate (N) (13.50 g, 49.20 mmol) was used instead of Intermediate (A).

LC-Mass (calculated: 260.10 g/mol, found: M⁺¹=261 g/mol).

(3) Synthesis of Intermediate (P)

Intermediate (P) (12.36 g, 25.73 mmol, yield=63%) was obtained in the same manner as used to synthesize Intermediate (D) of Synthesis Example 1, except that Intermediate (O) (10.62 g, 40.84 mmol) was used instead of Intermediate (B).

LC-Mass (calculated: 480.20 g/mol, found: M⁺¹=481 g/mol).

(4) Synthesis of Intermediate (Q)

Intermediate (Q) (5.44 g, 8.74 mmol, yield=84%) was obtained in the same manner as used to synthesize Intermediate (E) of Synthesis Example 1, except that Intermediate (P) (5.0 g, 10.40 mmol) was used instead of Intermediate (D).

(5) Synthesis of Compound 14

Compound 14 (2.40 g, 3.50 mmol, yield=40%) was obtained in the same manner as used to synthesize Compound 2 of Synthesis Example 1, except that Intermediate (Q) (5.44 g, 8.74 mmol) was used instead of Intermediate (E).

LC-Mass (calculated: 687.16 g/mol, found: M⁺¹=688 g/mol).

Synthesis Example 7 (Compound 12)

(1) Synthesis of Intermediate (S)

Intermediate (S) (5.87 g, 9.45 mmol, yield=63%) was obtained in the same manner as used to synthesize Intermediate (D) of Synthesis Example 1, except that Intermediate (R) (5.78 g, 15.00 mmol) was used instead of Intermediate (C).

LC-Mass (calculated: 620.35 g/mol, found: M⁺¹=621 g/mol).

(2) Synthesis of Intermediate (T)

Intermediate (T) (5.91 g, 7.75 mmol, yield=82%) was obtained in the same manner as used to synthesize Intermediate (E) of Synthesis Example 1, except that Intermediate (S) (5.87 g, 9.45 mmol) was used instead of Intermediate (D).

(3) Synthesis of Compound 12

Compound 12 (2.69 g, 3.26 mmol, yield=42%) was obtained in the same manner as used to synthesize Compound 2 of Synthesis Example 1, except that Intermediate (T) (5.91 g, 7.75 mmol) was used instead of Intermediate (E).

LC-Mass (calculated: 827.32 g/mol, found: M⁺¹=828 g/mol).

Synthesis Example 8 (Compound 21)

(1) Synthesis of Intermediate (U)

Intermediate (U) (4.99 g, 9.30 mmol, yield=62%) was obtained in the same manner as used to synthesize Intermediate (P) of Synthesis Example 6, except that Intermediate (F) (5.36 g, 15.00 mmol) was used instead of Intermediate (C).

LC-Mass (calculated: 536.26 g/mol, found: M⁺¹=537 g/mol).

(2) Synthesis of Intermediate (V)

Intermediate (V) (5.72 g, 7.72 mmol, yield=83%) was obtained in the same manner as used to synthesize Intermediate (M) of Synthesis Example 5, except that Intermediate (U) (4.99 g, 9.30 mmol) was used instead of Intermediate (G).

(3) Synthesis of Compound 21

Compound 21 (2.55 g, 3.17 mmol, yield=41%) was obtained in the same manner as used to synthesize Compound 2 of Synthesis Example 1, except that Intermediate (V) (5.72 g, 7.72 mmol) was used instead of Intermediate (E).

LC-Mass (calculated: 805.24 g/mol, found: M⁺¹=806 g/mol).

Evaluation Example 1: Evaluation of PL Spectrum

After Compound 2 was diluted to 10 mM in toluene, a PL spectrum was measured at room temperature using an ISC PC1 spectrofluorometer equipped with a Xenon lamp. The same experiment was performed on Compounds 3, 4, and 5. Results are shown in Table 2.

TABLE 2 Maximum emission wavelength Compound No. (nm) FWHM (nm) 2 457 21 3 461 24 4 461 24 5 461 24

From Table 2, it can be seen that Compounds 2, 3, 4, and 5 emit blue light having a narrow FWHM.

Example 1

A glass substrate, on which a 1500 Å-thick ITO (indium tin oxide) electrode (first electrode, anode) was formed, was cleaned by distilled water ultrasonication. After the distilled water ultrasonication, ultrasonic cleaning was performed with isopropyl alcohol, acetone, and methanol, sequentially in this stated order, and the glass substrate was dried and transferred to a plasma cleaner. The glass substrate was cleaned by using oxygen plasma for 5 minutes, and then transferred to a vacuum laminator.

Compound HT3 was vacuum-deposited on the ITO electrode of the glass substrate to form a first hole injection layer having a thickness of 3500 Å, Compound HT-D1 was vacuum-deposited on the first hole injection layer to form a second hole injection layer having a thickness of 300 Å, and TAPC was vacuum-deposited on the second hole injection layer to form an electron blocking layer having a thickness of 100 Å, thereby forming a hole transport region.

Compound H52 and Compound 2 (dopant, 10 wt %) were co-deposited on the hole transport region to form an emission layer having a thickness of 300 Å.

Compound ET3 was vacuum deposited on the emission layer to form an electron transport layer having a thickness of 250 Å, ET-D1 (Liq) was deposited on the electron transport layer to form an electron injection layer having a thickness of 5 Å, and an Al second electrode (cathode) having a thickness of 1000 Å was formed on the electron injection layer, thereby completing the manufacture of an organic light-emitting device.

Examples 2 to 6 and Comparative Examples (A) to (C)

Organic light-emitting devices were manufactured in the same manner as in Example 1, except that in forming an emission layer, for use as a dopant, corresponding compounds shown in Table 3 were used instead of Compound 2.

Evaluation Example 2: Evaluation on Characteristics of Organic Light-Emitting Device

Regarding the organic light-emitting devices manufactured according to Examples 1 to 6 and Comparative Examples (A) to (C), the maximum emission wavelength (nm) and FWHM of the EL spectrum, driving voltage (V), and external quantum efficiency (%) were evaluated. Results thereof are shown in Table 3. For each organic light-emitting device, the maximum emission wavelength and FWHM of the EL spectrum was evaluated from an EL spectrum (at 500 cd/m²) measured using a luminance meter (Minolta Cs-1000A). The driving voltage and the external quantum efficiency were evaluated by using a current-voltage meter (Keithley 2400) and a luminance meter (Minolta Cs-1000A), respectively. The driving voltage and external quantum efficiency of each of the organic light-emitting devices of Examples 1 to 6 and Comparative Examples (B) and (C) were expressed as relative values (%) with respect to the driving voltage and external quantum efficiency of the organic light-emitting device of Comparative Example (A).

TABLE 3 External quantum Efficiency Dopant Maximum Driving voltage (V) (EQE) compound emission (Relative (at 1000 cd/m²) No. wavelength (nm) FWHM (nm) value, %) (Relative value, %) Example 1 2 457 21 67 482 Example 2 3 461 24 69 550 Example 3 4 461 24 69 553 Example 4 5 461 24 69 556 Example 5 9 465 26 71 465 Example 6 12 461 24 70 523 Comparative (A) 488 78 100 100 Example (A) Comparative (B) 457 23 79 447 Example (B) Comparative (C) 454 43 85 243 Example (C)

From Table 3, it can be seen that the organic light-emitting devices of Example 1 to 6 emit blue light having a relatively small FWHM and have improved driving voltage and improved external quantum efficiency, at the same time, compared to the organic light-emitting device of Comparative Examples (A) to (C).

The organometallic compound according to embodiments has excellent electric characteristics and thermal stability. Accordingly, an organic light-emitting device including the organometallic compound may have better characteristics in terms of a driving voltage and external quantum efficiency.

It should be understood that embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments. While one or more embodiments have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details is made therein without departing from the spirit and scope of the disclosure as defined by the following claims. 

What is claimed is:
 1. An organometallic compound represented by Formula 1:

wherein, in Formula 1, M is a transition metal, X₁ is C, and X₂ to X₄ are each independently C or N, a bond between X₁ and M is a coordinate bond, one of a bond between X₂ and M, a bond between X₃ and M, and a bond between X₄ and M is a coordinate bond, and the other two bonds are covalent bonds, X₁₁ is O, S, or N(R_(1a)), a group represented by

is a group represented by one of Formulae CY1-5 to CY1-15,

wherein, in Formulae CY1-5 to CY1-15, R₁₁ to R₁₄ are each independently an unsubstituted or substituted C₁-C₆₀ alkyl group or an unsubstituted or substituted C₃-C₁₀ cycloalkyl group, * indicates a binding site to M in Formula 1, and *′ indicates a binding site to ring CY₂ in Formula 1, ring CY₂ to ring CY₄ are each independently a C₅-C₃₀ carbocyclic group or a C₁-C₃₀ heterocyclic group, T₁ is a single bond, a double bond, *—N(R₅)—*′, *—B(R₅)—*′, *—P(R₅)—*′, *—C(R₅) (R₆)—*′, *—Si(R₅)(R₆)—*′, *—Ge(R₅)(R₆)—*′, *—S—*′, *—Se—*′, *—O—*′, *—C(═O)—*′, *—S(═O)—*′, *—S(═O)₂—*′, *—C(R₅)═*′, *═C(R₅)—*′, *—C(R₅)═C(R₆)—*′, *—C(═S)—*′, or *—C≡C—*′, T₂ is a single bond, a double bond, *—N(R₇)—*′, *—B(R₇)—*′, *—P(R₇)—*′, *—C(R₇) (R₈)—*′, *—Si(R₇)(R₈)—*′, *—Ge(R₇)(R₈)—*′, *—S—*′, *—Se—*′, *—O—*′, *—C(═O)—*′, *—S(═O)—*′, *—S(═O)₂—*′, *—C(R₇)═*′, *═C(R₇)—*′, *—C(R₇)═C(R₈)—*′, *—C(═S)—*′, or *C≡C—*′, R_(1a), R₁ to R₈ are each independently hydrogen, deuterium, —F, —Cl, —Br, —I, —SF₅, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a substituted or unsubstituted C₁-C₆₀ alkyl group, a substituted or unsubstituted C₂-C₆₀ alkenyl group, a substituted or unsubstituted C₂-C₆₀ alkynyl group, a substituted or unsubstituted C₁-C₆₀ alkoxy group, a substituted or unsubstituted C₁-C₆₀ alkylthio group, a substituted or unsubstituted C₃-C₁₀ cycloalkyl group, a substituted or unsubstituted C₁-C₁₀ heterocycloalkyl group, a substituted or unsubstituted C₃-C₁₀ cycloalkenyl group, a substituted or unsubstituted C₂-C₁₀ heterocycloalkenyl group, a substituted or unsubstituted C₆-C₆₀ aryl group, a substituted or unsubstituted C₇-C₆₀ alkylaryl group, a substituted or unsubstituted C₆-C₆₀ aryloxy group, a substituted or unsubstituted C₆-C₆₀ arylthio group, a substituted or unsubstituted C₁-C₆₀ heteroaryl group, a substituted or unsubstituted C₂-C₆₀ alkyl heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, —N(Q₁)(Q₂), —Si(Q₃)(Q₄)(Q₅), —Ge(Q₃)(Q₄)(Q₅), —B(Q₆)(Q₇), —P(═O)(Q₈)(Q₉), or —P(Q₈)(Q₉), a1 is an integer from 1 to 4, a2 to a4 are each independently an integer from 0 to 20, at least one of R₁ in the number of a1 is each independently an unsubstituted or substituted C₁-C₆₀ alkyl group or an unsubstituted or substituted C₃-C₁₀ cycloalkyl group, two or more of a plurality of R₁(s) are optionally linked to each other to form a C₅-C₃₀ carbocyclic group unsubstituted or substituted with at least one R_(10a) or a C₁-C₃₀ heterocyclic group unsubstituted or substituted with at least one R_(10a), two or more of a plurality of R₂(s) are optionally linked to each other to form a C₅-C₃₀ carbocyclic group unsubstituted or substituted with at least one R_(10a) or a C₁-C₃₀ heterocyclic group unsubstituted or substituted with at least one R_(10a), two or more of a plurality of R₃(s) are optionally linked to each other to form a C₅-C₃₀ carbocyclic group unsubstituted or substituted with at least one R_(10a) or a C₁-C₃₀ heterocyclic group unsubstituted or substituted with at least one R_(10a), two or more of a plurality of R₄(s) are optionally linked to each other to form a C₅-C₃₀ carbocyclic group unsubstituted or substituted with at least one R_(10a) or a C₁-C₃₀ heterocyclic group unsubstituted or substituted with at least one R_(10a), two or more of R_(1a) and R₁ to R₈ are optionally linked to each other to form a C₅-C₃₀ carbocyclic group unsubstituted or substituted with at least one R_(10a) or a C₁-C₃₀ heterocyclic group unsubstituted or substituted with at least one R_(10a), R_(10a) is the same as described in connection with R₂, * and *′ each indicate a binding site to a neighboring atom, a substituent of the substituted C₁-C₆₀ alkyl group, the substituted C₂-Coo alkenyl group, the substituted C₂-C₆₀ alkynyl group, the substituted C₁-C₆₀ alkoxy group, the substituted C₁-C₆₀ alkylthio group, the substituted C₃-C₁₀ cycloalkyl group, the substituted C₁-C₁₀ heterocycloalkyl group, the substituted with C₃-C₁₀ cycloalkyl group, the substituted C₂-C₁₀ heterocycloalkenyl group, the substituted C₆-C₆₀ aryl group, the substituted, a C₇-C₆₀ alkylaryl group, the substituted C₆-C₆₀ aryloxy group, the substituted C₆-C₆₀ arylthio group, the substituted C₁-C₆₀ heteroaryl group, the substituted C₂-C₆₀ alkylheteroaryl group, the substituted monovalent non-aromatic condensed polycyclic group, and the substituted monovalent non-aromatic condensed heteropolycyclic group is: deuterium, —F, —Cl, —Br, —I, -CD₃, -CD₂H, -CDH₂, —CF₃, —CF₂H, —CFH₂, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C₁-C₆₀ alkyl group, a C₂-C₆₀ alkenyl group, a C₂-C₆₀ alkynyl group, or a C₁-C₆₀ alkoxy group; a C₁-C₆₀ alkyl group, a C₂-C₆₀ alkenyl group, a C₂-C₆₀ alkynyl group, or a C₁-C₆₀ alkoxy group, each substituted with deuterium, —F, —Cl, —Br, —I, -CD₃, -CD₂H, -CDH₂, —CF₃, —CF₂H, —CFH₂, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C₃-C₁₀ cycloalkyl group, a C₁-C₁₀ heterocycloalkyl group, a C₃-C₁₀ cycloalkenyl group, a C₂-C₁₀ heterocycloalkenyl group, a C₆-C₆₀ aryl group, a C₆-C₆₀ aryloxy group, a C₆-C₆₀ arylthio group, a C₁-C₆₀ heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, —N(Q₁₁)(Q₁₂), —Si(Q₁₃)(Q₁₄)(Q₁₅), —Ge(Q₁₃)(Q₁₄)(Q₁₅), —B(Q₁₆)(Q₁₇), —P(═O)(Q₁₈)(Q₁₉), —P(Q₁₈)(Q₁₉), or any combination thereof; a C₃-C₁₀ cycloalkyl group, a C₁-C₁₀ heterocycloalkyl group, a C₃-C₁₀ cycloalkenyl group, a C₂-C₁₀ heterocycloalkenyl group, a C₆-C₆₀ aryl group, a C₆-C₆₀ aryloxy group, a C₆-C₆₀ arylthio group, a C₁-C₆₀ heteroaryl group, a monovalent non-aromatic condensed polycyclic group, or a monovalent non-aromatic condensed heteropolycyclic group, each unsubstituted or substituted with deuterium, —F, —Cl, —Br, —I, -CD₃, -CD₂H, -CDH₂, —CF₃, —CF₂H, —CFH₂, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C₁-C₆₀ alkyl group, a C₂-C₆₀ alkenyl group, a C₂-C₆₀ alkynyl group, a C₁-C₆₀ alkoxy group, a C₃-C₁₀ cycloalkyl group, a C₁-C₁₀ heterocycloalkyl group, a C₃-C₁₀ cycloalkenyl group, a C₂-C₁₀ heterocycloalkenyl group, a C₆-C₆₀ aryl group, a C₆-C₆₀ aryloxy group, a C₆-C₆₀ arylthio group, a C₁-C₆₀ heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, —N(Q₂₁)(Q₂₂), —Si(Q₂₃)(Q₂₄)(Q₂₅), —Ge(Q₂₃)(Q₂₄)(Q₂₅), —B(Q₂₆)(Q₂₇), —P(═O)(Q₂₈)(Q₂₉), —P(Q₂₈)(Q₂₉), or any combination thereof; —N(Q₃₁)(Q₃₂), —Si(Q₃₃)(Q₃₄)(Q₃₅), —Ge(Q₃₃)(Q₃₄)(Q₃₅), —B(Q₃₆)(Q₃₇), —P(═O)(Q₃₈)(Q₃₉), or —P(Q₃₈)(Q₃₉); or any combination thereof, wherein Q₁ to Q₉, Q₁₁ to Q₁₉, Q₂₁ to Q₂₉ and Q₃₁ to Q₃₉ are each independently hydrogen; deuterium; —F; —Cl; —Br; —I; a hydroxyl group; a cyano group; a nitro group; an amidino group; a hydrazine group; a hydrazone group; a carboxylic acid group or a salt thereof; a sulfonic acid group or a salt thereof; a phosphoric acid group or a salt thereof; a C₁-C₆₀ alkyl group that is unsubstituted or substituted with deuterium, a C₁-C₆₀ alkyl group, a C₆-C₆₀ aryl group, or any combination thereof; a C₂-C₆₀ alkenyl group; a C₂-C₆₀ alkynyl group; a C₁-C₆₀ alkoxy group; a C₃-C₁₀ cycloalkyl group; a C₁-C₁₀ heterocycloalkyl group; a C₃-C₁₀ cycloalkenyl group; a C₂-C₁₀ heterocycloalkenyl group; a C₆-C₆₀ aryl group that is unsubstituted or substituted with deuterium, a C₁-C₆₀ alkyl group, a C₆-C₆₀ aryl group, or any combination thereof; a C₆-C₆₀ aryloxy group; a C₆-C₆₀ arylthio group; a C₁-C₆₀ heteroaryl group; a monovalent non-aromatic condensed polycyclic group; or a monovalent non-aromatic condensed heteropolycyclic group.
 2. The organometallic compound of claim 1, wherein M is Pt, Pd, or Au.
 3. The organometallic compound of claim 1, wherein X₂ and X₃ are each C, X₄ is N, a bond between X₂ and M and a bond between X₃ and M are each a covalent bond, and a bond between X₄ and M is a coordinate bond.
 4. The organometallic compound of claim 1, wherein ring CY₂ to ring CY₄ are each independently i) a first ring, ii) a second ring, iii) a condensed ring in which two or more first rings are condensed with each other, iv) a condensed ring in which two or more second rings are condensed with each other, or v) a condensed ring in which one or more first rings and one or more second rings are condensed with each other, the first ring is a cyclopentane group, a cyclopentadiene group, a furan group, a thiophene group, a pyrrole group, a silole group, an oxazole group, an isoxazole group, an oxadiazole group, an isoxadiazole group, an oxatriazole group, an isoxatriazole group, a thiazole group, an isothiazole group, a thiadiazole group, an isothiadiazole group, a thiatriazole group, an isothiatriazole group, a pyrazole group, an imidazole group, a triazole group, a tetrazole group, an azasilole group, a diazasilole group, or a triazasilole group, and the second ring is an adamantane group, a norbornane group, a norbornene group, a cyclohexane group, a cyclohexene group, a benzene group, a pyridine group, a pyrimidine group, a pyrazine group, a pyridazine group, a triazine group, an oxazine group, a thiazine group, a dihydropyrazine group, a dihydropyridine group, or a dihydroazasilole group.
 5. The organometallic compound of claim 1, wherein T₁ is *—N(R₅)—*′, *—C(R₅)(R₆)—*′, *—S—*, *—O—*′, or *—S(═O)₂—*′, and T₂ is a single bond, *—N(R₇)—*′, *—C(R₇)(R₈)—*′, *—S—*′, or *—O—*′.
 6. The organometallic compound of claim 1, wherein R_(1a), R₁, R₃ and R₅ to R₈ are each independently: hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, —SF₅, C₁-C₂₀ alkyl group, a C₂-C₂₀ alkenyl group, a C₁-C₂₀ alkoxy group, or a C₁-C₂₀ alkylthio group; a C₁-C₂₀ alkyl group, a C₂-C₂₀ alkenyl group, a C₁-C₂₀ alkoxy group, or a C₁-C₂₀ alkylthio group, each unsubstituted or substituted with deuterium, —F, —Cl, —Br, —I, -CD₃, —CD₂H, -CDH₂, —CF₃, —CF₂H, —CFH₂, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C₁-C₁₀ alkyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a bicyclo[1.1.1]pentyl group, a bicyclo[2.1.1]hexyl group, a bicyclo[2.2.2]octyl group, a (C₁-C₂₀ alkyl)cyclopentyl group, a (C₁-C₂₀ alkyl)cyclohexyl group, a (C₁-C₂₀ alkyl)cycloheptyl group, a (C₁-C₂₀ alkyl)cyclooctyl group, a (C₁-C₂₀ alkyl)adamantanyl group, a (C₁-C₂₀ alkyl)norbornanyl group, a (C₁-C₂₀ alkyl)norbornenyl group, a (C₁-C₂₀ alkyl)cyclopentenyl group, a (C₁-C₂₀ alkyl)cyclohexenyl group, a (C₁-C₂₀ alkyl)cycloheptenyl group, a (C₁-C₂₀ alkyl)bicyclo[1.1.1]pentyl group, a (C₁-C₂₀ alkyl)bicyclo[2.1.1]hexyl group, a (C₁-C₂₀ alkyl)bicyclo[2.2.2]octyl group, a phenyl group, a (C₁-C₂₀ alkyl)phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a pyridinyl group, a pyrimidinyl group, or any combination thereof; a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a bicyclo[1.1.1]pentyl group, a bicyclo[2.1.1]hexyl group, a bicyclo[2.2.2]octyl group, a phenyl group, a (C₁-C₂₀ alkyl)phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthrolinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, an azacarbazolyl group, an azadibenzofuranyl group, or an azadibenzothiophenyl group, each unsubstituted or substituted with deuterium, —F, —Cl, —Br, —I, -CD₃, -CD₂H, -CDH₂, —CF₃, —CF₂H, —CFH₂, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C₁-C₂₀ alkyl group, deuterated C₂-C₂₀ alkyl group, a C₁-C₂₀ alkoxy group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a bicyclo[1.1.1]pentyl group, a bicyclo[2.1.1]hexyl group, a bicyclo[2.2.2]octyl group, a (C₁-C₂₀ alkyl)cyclopentyl group, a (C₁-C₂₀ alkyl)cyclohexyl group, a (C₁-C₂₀ alkyl)cycloheptyl group, a (C₁-C₂₀ alkyl)cyclooctyl group, a (C₁-C₂₀ alkyl)adamantanyl group, a (C₁-C₂₀ alkyl)norbornanyl group, a (C₁-C₂₀ alkyl)norbornenyl group, a (C₁-C₂₀ alkyl)cyclopentenyl group, a (C₁-C₂₀ alkyl)cyclohexenyl group, a (C₁-C₂₀ alkyl)cycloheptenyl group, a (C₁-C₂₀ alkyl)bicyclo[1.1.1]pentyl group, a (C₁-C₂₀ alkyl)bicyclo[2.1.1]hexyl group, a (C₁-C₂₀ alkyl)bicyclo[2.2.2]octyl group, a phenyl group, a (C₁-C₂₀ alkyl)phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthrolinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, an azacarbazolyl group, an azadibenzofuranyl group, an azadibenzothiophenyl group, or any combination thereof; or —N(Q₁)(Q₂), —Si(Q₃)(Q₄)(Q₅), —Ge(Q₃)(Q₄)(Q₅), —B(Q₆)(Q₇), —P(═O)(Q₈)(Q₉), or —P(Q₈)(Q₉), R₂ and R₄ are each independently: hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, —SF₅, C₁-C₂₀ alkyl group, a C₂-C₂₀ alkenyl group, a C₁-C₂₀ alkoxy group, or a C₁-C₂₀ alkylthio group; a C₁-C₂₀ alkyl group, a C₂-C₂₀ alkenyl group, a C₁-C₂₀ alkoxy group, or a C₁-C₂₀ alkylthio group, each unsubstituted or substituted with deuterium, —F, —Cl, —Br, —I, -CD₃, -CD₂H, -CDH₂, —CF₃, —CF₂H, —CFH₂, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C₁-C₁₀ alkyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a bicyclo[1.1.1]pentyl group, a bicyclo[2.1.1]hexyl group, a bicyclo[2.2.2]octyl group, a (C₁-C₂₀ alkyl)cyclopentyl group, a (C₁-C₂₀ alkyl)cyclohexyl group, a (C₁-C₂₀ alkyl)cycloheptyl group, a (C₁-C₂₀ alkyl)cyclooctyl group, a (C₁-C₂₀ alkyl)adamantanyl group, a (C₁-C₂₀ alkyl)norbornanyl group, a (C₁-C₂₀ alkyl)norbornenyl group, a (C₁-C₂₀ alkyl)cyclopentenyl group, a (C₁-C₂₀ alkyl)cyclohexenyl group, a (C₁-C₂₀ alkyl)cycloheptenyl group, a (C₁-C₂₀ alkyl)bicyclo[1.1.1]pentyl group, a (C₁-C₂₀ alkyl)bicyclo[2.1.1]hexyl group, a (C₁-C₂₀ alkyl)bicyclo[2.2.2]octyl group, a phenyl group, a (C₁-C₂₀ alkyl)phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a pyridinyl group, a pyrimidinyl group, or any combination thereof; a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a bicyclo[1.1.1]pentyl group, a bicyclo[2.1.1]hexyl group, a bicyclo[2.2.2]octyl group, each unsubstituted or substituted with deuterium, —F, —Cl, —Br, —I, -CD₃, -CD₂H, -CDH₂, —CF₃, —CF₂H, —CFH₂, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C₁-C₂₀ alkyl group, deuterated C₂-C₂₀ alkyl group, a C₁-C₂₀ alkoxy group, or any combination thereof; or —N(Q₁)(Q₂), —Si(Q₃)(Q₄)(Q₅), —Ge(Q₃)(Q₄)(Q₅), —B(Q₆)(Q₇), —P(═O)(Q₈)(Q₉), or —P(Q₈)(Q₉), and Q₁ to Q₉ are each independently: deuterium, —F, —CH₃, —CD₃, —CD₂H, —CDH₂, —CH₂CH₃, —CH₂CD₃, —CH₂CD₂H, —CH₂CDH₂, —CHDCH₃, —CHDCD₂H, —CHDCDH₂, —CHDCD₃, —CD₂CD₃, —CD₂CD₂H, —CD₂CDH₂, —CF₃, —CF₂H, —CFH₂, —CH₂CF₃, —CH₂CF₂H, —CH₂CFH₂, —CHFCH₃, —CHFCF₂H, —CHFCFH₂, —CHFCF₃, —CF₂CF₃, —CF₂CF₂H, or —CF₂CFH₂; or an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, an isobutyl group, a tert-butyl group, an n-pentyl group, a tert-pentyl group, a neopentyl group, an isopentyl group, a sec-pentyl group, 3-pentyl group, a sec-isopentyl group, a phenyl group, a biphenyl group, or a naphthyl group, each unsubstituted or substituted with deuterium, —F, a C₁-C₁₀ alkyl group, a phenyl group, or any combination thereof.
 7. The organometallic compound of claim 1, wherein a1 is 1 or
 2. 8. The organometallic compound of claim 1, wherein at least one of R₁(s) in the number of a1 is each independently a C₁-C₂₀ alkyl group or a C₃-C₁₀ cycloalkyl group, each unsubstituted or substituted with deuterium, —F, —Cl, —Br, —I, —CD₃, —CD₂H, —CDH₂, —CF₃, —CF₂H, —CFH₂, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C₁-C₁₀ alkyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a bicyclo[1.1.1]pentyl group, a bicyclo[2.1.1]hexyl group, a bicyclo[2.2.2]octyl group, a (C₁-C₂₀ alkyl)cyclopentyl group, a (C₁-C₂₀ alkyl)cyclohexyl group, a (C₁-C₂₀ alkyl)cycloheptyl group, a (C₁-C₂₀ alkyl)cyclooctyl group, a (C₁-C₂₀ alkyl)adamantanyl group, a (C₁-C₂₀ alkyl)norbornanyl group, a (C₁-C₂₀ alkyl)norbornenyl group, a (C₁-C₂₀ alkyl)cyclopentenyl group, a (C₁-C₂₀ alkyl)cyclohexenyl group, a (C₁-C₂₀ alkyl)cycloheptenyl group, a (C₁-C₂₀ alkyl)bicyclo[1.1.1]pentyl group, a (C₁-C₂₀ alkyl)bicyclo[2.1.1]hexyl group, a (C₁-C₂₀ alkyl)bicyclo[2.2.2]octyl group, or any combination thereof.
 9. The organometallic compound of claim 1, wherein at least one of R₂(s) in the number of a2, at least one of R₄(s) in the number of a4, or any combination thereof is each independently an unsubstituted or substituted C₁-C₆₀ alkyl group or an unsubstituted or substituted C₃-C₁₀ cycloalkyl group.
 10. The organometallic compound of claim 1, wherein a group represented by

is represented by one of Formulae A2-1(1) to A2-1(17):

wherein, in Formulae A2-1(1) to A2-1(17), X₂ and R₂ are respectively the same as described in claim 1, X₂₁ is a single bond, O, S, N(R₂₁), C(R₂₁)(R₂₂), or Si(R₂₁)(R₂₂), and X₂₂ is a single bond, O, S, N(R₂₃), C(R₂₃)(R₂₄), or Si(R₂₃)(R₂₄), wherein at least one of X₂₁ and X₂₂ is not a single bond, R₂₁ to R₂₈ are the same as described in connection with R₂ in claim 1, a25 is an integer from 0 to 5, a24 is an integer from 0 to 4, a23 is an integer from 0 to 3, a22 is an integer from 0 to 2, * indicates a binding site to M in Formula 1, *′ indicates a binding site to a neighboring nitrogen atom in Formula 1, and *″ indicates a binding site to T₁ in Formula
 1. 11. The organometallic compound of claim 1, wherein a group represented by

is a group represented by one of Formulae A3-1(1) to A3-1(17) and A3-2(1) to A3-2(7):

wherein, in Formulae A3-1(1) to A3-1(17) and A3-2(1) to A3-2(7), X₃ and R₃ are the same as described in claim 1, X₃₁ is a single bond, O, S, N(R₃₁), C(R₃₁)(R₃₂), or Si(R₃₁)(R₃₂), X₃₂ is a single bond, O, S, N(R₃₃), C(R₃₃)(R₃₄), or Si(R₃₃)(R₃₄), and at least one of X₃₁ and X₃₂ of Formulae A3-1(16) and A3-1(17) is not a single bond, R₃₁ to R₃₈ are the same as described in connection with R₃ in claim 1, a36 is an integer from 0 to 6, a35 is an integer from 0 to 5, a34 is an integer from 0 to 4, a33 is an integer from 0 to 3, a32 is an integer from 0 to 2, * indicates a binding site to M in Formula 1, *′ indicates a binding site to T₂ in Formula 1, and *″ indicates a binding site to T₁ in Formula
 1. 12. The organometallic compound of claim 1, wherein a group represented by

is a group represented by one of Formulae A4-1(1) to A4-1(26) and A4-2(1) to A4-2(8):

wherein, in Formulae A4-1(1) to A4-1(26) and A4-2(1) to A4-2(8), X₄ and R₄ are respectively the same as described in claim 1, X₄₁ is a single bond, O, S, N(R₄₁), C(R₄₁)(R₄₂), or Si(R₄₁)(R₄₂), X₄₂ is a single bond, O, S, N(R₄₃), C(R₄₃)(R₄₄), or Si(R₄₃)(R₄₄), and at least one of X₄₁ and X₄₂ of Formulae A4-1(24) to A4-1(26) is not a single bond, R₄₁ to R₄₈ are the same as described in connection with R₄ in claim 1, a46 is an integer from 0 to 6, a45 is an integer from 0 to 5, a44 is an integer from 0 to 4, a43 is an integer from 0 to 3, a42 is an integer from 0 to 2, * indicates a binding site to M in Formula 1, and *′ indicates a binding site to T₂ in Formula
 1. 13. The organometallic compound of claim 1, wherein a group represented by

is a group represented by one of Formulae CY2-1 to CY2-8, a group represented by

is a group represented by one of Formulae CY3-1 to CY3-16, a group represented by

is a group represented by one of Formulae CY4-1 to CY4-24:

wherein, in Formulae CY2-1 to CY2-8, CY3-1 to CY3-16, and CY4-1 to CY4-24, X₂ to X₄ are respectively the same as described in claim 1, X₃₁ is a single bond, O, S, N(R₃₁), C(R₃₁)(R₃₂), or Si(R₃₁)(R₃₂), X₄₁ is a single bond, O, S, N(R₄₁), C(R₄₁)(R₄₂), or Si(R₄₁)(R₄₂), R₂₁ to R₂₃ are the same as described in connection with R₂ in claim 1, R₃₁ to R₃₆ are the same as described in connection with R₃ in claim 1, R₄₁ to R₄₄ are the same as described in connection with R₄ in claim 1, and each of R₂₁ to R₂₃, R₃₁ to R₃₆, and R₄₁ to R₄₄ is not hydrogen, in Formulae CY1-1 to CY1-15, * indicates a binding site to M in Formula 1, and *′ indicates a binding site to ring CY₂ in Formula 1, in Formulae CY2-1 to CY2-8, * indicates a binding site to M in Formula 1, *′ indicates a binding site to a neighboring nitrogen atom in Formula 1, and *″ indicates a binding site to T₁ in Formula 1, in Formulae CY3-1 to CY3-16, * indicates a binding site to M in Formula 1, *″ indicates a binding site to T₁ in Formula 1, and *′ indicates a binding site to T₂ in Formula 1, and in Formulae CY4-1 to CY4-24, * indicates a binding site to M in Formula 1, and *′ indicates a binding site to T₂ in Formula
 1. 14. The organometallic compound of claim 1, wherein the organometallic compound is represented by one of Formulae 1A to 1C:

wherein, in Formulae 1A to 1C, M, X₁ to X₄, X₁₁, T₁, and T₂ are the same as described in claim 1, and T₂ in Formula 1C is not a single bond, Y₂₁ is C(R₂₁) or N, Y₂₂ is C(R₂₂) or N, Y₂₃ is C(R₂₃) or N, Y₃₁ is C(R₃₁) or N, Y₃₂ is C(R₃₂) or N, Y₃₃ is C(R₃₃) or N, Y₃₄ is C(R₃₄) or N, Y₃₅ is C(R₃₅) or N, Y₃₆ is C(R₃₆) or N, Y₄₁ is C(R₄₁) or N, Y₄₂ is C(R₄₂) or N, Y₄₃ is C(R₄₃) or N, Y₄₄ is C(R₄₄) or N, Y₄₅ is C(R₄₅) or N, Y₄₆ is C(R₄₆) or N, Y₄₇ is C(R₄₇) or N, X₃₃ is a single bond, O, S, N(R_(3a)), C(R_(3a))(R_(3b)), or Si(R_(3a))(R_(3b)), X₄₃ is a single bond, O, S, N(R_(4a)), C(R_(4a))(R_(4b)), or Si(R_(4a))(R_(4b)), R₁₁ to R₁₄ are the same as described in claim 1, R₂₁ to R₂₃ are the same as described in connection with R₂ in claim 1, and two or more of R₂₁ to R₂₃ are optionally linked to form a C₅-C₃₀ carbocyclic group unsubstituted or substituted with at least one R_(10a), or a C₁-C₃₀ heterocyclic group unsubstituted or substituted with at least one R_(10a), R₃₁ to R₃₆, R_(3a), and R_(3b) are the same as described in connection with R₃ in claim 1, and two or more of R₃₁ to R₃₆ are optionally linked to form a C₅-C₃₀ carbocyclic group unsubstituted or substituted with at least one R_(10a) or a C₁-C₃₀ heterocyclic group unsubstituted or substituted with at least one R_(10a), R₄₁ to R₄₇, R_(4a), and R_(4b) are the same as described in connection with R₄ in claim 1, and two or more of R₄₁ to R₄₇ are optionally linked to form a C₅-C₃₀ carbocyclic group unsubstituted or substituted with at least one R_(10a) or a C₁-C₃₀ heterocyclic group unsubstituted or substituted with at least one R_(10a), and R_(10a) is the same as described in connection with R₂ in claim
 1. 15. The organometallic compound of claim 1, wherein the organometallic compound emits blue light.
 16. The organometallic compound of claim 1, wherein the organometallic compound is one of Compounds 2 to 5, 9 to 10, 14 to 17, 21 to 22, 26 to 29, 33 to 34, 38 to 41, 45 to 46, 50 to 53, 57 to 58, 62 to 65, 69 to 70, 74 to 77, 81 to 82, 86 to 89, 93 to 94, 98 to 101, 105 to 106, 110 to 113, and 117 to 118:


17. An organic light-emitting device comprising: a first electrode; a second electrode; and an organic layer disposed between the first electrode and the second electrode, wherein the organic layer comprises at least one organometallic compound of claim
 1. 18. The organic light-emitting device of claim 17, wherein the first electrode is an anode, the second electrode is a cathode, the organic layer comprises a hole transport region disposed between the first electrode and the emission layer and an electron transport region disposed between the emission layer and the second electrode, the hole transport region comprises a hole injection layer, a hole transport layer, an electron blocking layer, or any combination thereof, and the electron transport region comprises a hole blocking layer, an electron transport layer, an electron injection layer, or any combination thereof.
 19. The organic light-emitting device of claim 17, wherein the organometallic compound is included in the emission layer.
 20. The organic light-emitting device of claim 19, wherein the emission layer emits blue light. 